BOSTON — Called upon to console a grieving city and reassure a shaken nation, President Barack Obama on Thursday promised that Boston would "run again" after deadly twin bombings at its famous marathon. More than 2,000 people rose in a standing ovation in the Cathedral of the Holy Cross and sang "America the Beautiful."

Obama's message of resolve in time of tragedy was echoed by Mayor Thomas Menino and Gov. Deval Patrick at a packed interfaith service.

"Nothing will take us down because we take care of one another," Menino said. "Even with the smell of smoke in the air and blood in the streets and tears in our eyes, we triumphed over that hateful act."

Three people were killed and more than 170 others were injured, some of them grievously, in Monday's bombings near the race's finish line.

Obama spoke just hours before the FBI released photographs and video of two suspects and asked for the public's help in identifying them.

In the midst of an emotional and trying stretch for the country and his presidency, Obama vowed to track down those responsible and lauded Boston's "undaunted" spirit.

"Your resolve is the greatest rebuke to whoever committed this heinous act," he told the gathering.

Indeed, Obama's words underscored the stark reality that has left many Americans jittery. Even as authorities narrowed their search to two men captured on video, the suspects remained at large and their motives were still a mystery.

For Obama, the bombings began a week consumed not only by terror but also disaster and political defeat. Letters sent to Washington officials, including Obama and Sen. Roger Wicker, R-Miss., were found to contain traces of poisonous ricin in tests, evoking eerie parallels to the anthrax attacks that followed the terror of Sept. 11, 2001.

The president also lost a fight for new gun control measures in the Senate, then awoke Thursday to news of a powerful fertilizer plant explosion that devastated a small Texas town.

Speaking from the pulpit in the soaring cathedral, the president didn't explicitly declare the deadly marathon explosions an "act of terror" as he did earlier in the week during remarks at the White House. But he showed little restraint in describing those responsible for the attack, calling them "small, stunted individuals."

"Yes, we will find you, and yes, you will face justice," he said, as the crowd – some wearing bright yellow marathon jackets – applauded.

Also in the crowd was Obama's former presidential rival, Mitt Romney, who served one term as Massachusetts governor. Several state officials, including Democratic Sens. Elizabeth Warren and William "Mo" Cowan, traveled to Boston with Obama on Air Force One, as did Vicki Kennedy, the widow of the late Massachusetts icon, Sen. Ted Kennedy.

The president spoke of Boston in personal terms, reminding the audience of the years he spent in the city as a student at Harvard Law School. Boston was also the host for the 2004 Democratic National Convention that featured Obama as the keynote speaker, a role that would thrust the little-known Illinois state senator into the national spotlight.

Obama and first lady Michelle Obama sat at the front of the church next to Patrick. A mournful string solo by cellist Yo-Yo Ma preceded the governor's own remarks.

"We will grieve our losses and heal," Patrick said. "We will rise, and we will endure. We will have accountability without vengeance, vigilance without fear."

Thursday's service included reflections by representatives of Protestant denominations, the Jewish, Muslim and Greek Orthodox faiths, and Cardinal Sean O'Malley, head of the Roman Catholic church in Boston.

The event was open to the public on a first-come, first-seated basis, but the line to try to get a ticket stretched at least two city blocks. There was a heavy police presence around the cathedral in the city's South End, and authorities closed nearby streets to traffic.

"I think it's important that we heal as well as those who were affected. I guess sometimes you feel you can't do a single thing, and this is something we can do," said Beth Anne Stevenson, a Boston Medical Center surgical intensive care unit nurse.

Ricky Hall, 67, of Cambridge, showed up at 8 a.m. and stayed even after he believed he wouldn't get inside.

"I came to pay my respects to the victims," he said.

Following the 90-minute service, Warren urged Bostonians not to succumb to fear.

"We will be vigilant but we will not be afraid," she said.

The Obamas met privately with the family of Krystle Campbell, 29, who was among those killed in the attack. The Obamas also visited with many of the injured in their hospital rooms at Massachusetts General Hospital and thanked the marathon volunteers who rushed toward danger to help the wounded.

Separately, the first lady met with patients, their families and hospital staff at Boston Children's Hospital and Brigham and Women's Hospital.

Obama has played this role before, serving as the nation's consoler in chief at times of heartbreaking tragedy. He's grieved with the families of those killed in shootings at Newtown, Conn., Tucson, Ariz., Aurora, Colo., and Fort Hood, Texas. And he's comforted residents in tornado-ravaged Missouri and storm-ravaged communities in New York and New Jersey.

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Associated Press writer Bridget Murphy contributed to this report.

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Follow Julie Pace on Twitter: http://twitter.com/jpaceDC

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  • In this photo provided by The Daily Free Press and Kenshin Okubo, people react to an explosion at the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/The Daily Free Press, Kenshin Okubo) MANDATORY CREDIT

  • Medical workers aid injured people at the finish line of the 2013 Boston Marathon following an explosion Monday, April 15, 2013 in Boston. Two bombs exploded near the finish line of the marathon on Monday, killing at least two people, injuring at least 22 others and sending authorities rushing to aid wounded spectators. (AP Photo/Charles Krupa)

  • Boston police clear an area following an explosion near the finish line of the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/Charles Krupa)

  • Medical personnel work outside the medical tent in the aftermath of two blasts which exploded near the finish line of the Boston Marathon in Boston, Monday, April 15, 2013. (AP Photo/Elise Amendola)

  • An unidentified Boston Marathon runner, center, is reunited with loved ones near Copley Square following an explosion in Boston Monday, April 15, 2013. (AP Photo/Winslow Townson)

  • Medical workers aid an injured woman at the finish line of the 2013 Boston Marathon following two explosions there, Monday, April 15, 2013 in Boston. Two bombs exploded near the finish of the Boston Marathon on Monday, killing at least two people, injuring at least 23 others and sending authorities rushing to aid wounded spectators. (AP Photo/Charles Krupa)

  • Workers aid injured people at the finish line of the 2013 Boston Marathon following an explosion in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/The Boston Herald, Stuart Cahill) MANDATORY CREDIT

  • In this photo provided by The Daily Free Press and Kenshin Okubo, people react to an explosion at the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/The Daily Free Press, Kenshin Okubo) MANDATORY CREDIT

  • In this photo provided by The Daily Free Press and Kenshin Okubo, people react to an explosion at the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/The Daily Free Press, Kenshin Okubo) MANDATORY CREDIT

  • In this photo provided by The Daily Free Press and Kenshin Okubo, people assist an injured after an explosion at the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/The Daily Free Press, Kenshin Okubo) MANDATORY CREDIT

  • Medical workers aid an injured woman at the scene of a bomb blast near the finish line of the 2013 Boston Marathon following an explosion in Boston, Monday, April 15, 2013. Two bombs exploded near the finish line of the Boston Marathon on Monday, killing at least two people and injuring at scores of others (AP Photo/Charles Krupa)

  • Medical workers aid injured people at the finish line of the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two bombs exploded near the finish line of the Boston Marathon on Monday, killing at least two people and injuring dozens of others (AP Photo/Charles Krupa)

  • Runners who were diverted from the race course walk on the Commonwealth Mall two blocks from the site of an explosion at the finish line of the Boston Marathon in Boston, Monday, April 15, 2013. Two bombs exploded near the finish line of the Boston Marathon on Monday, killing at least two people and injuring at least 23 others. (AP Photo/Michael Dwyer)

  • Una mujer llora afectada por una explosión mientras caminan cerca de la línea de meta de la Maratón de Boston el lunes 15 de abril de 2013. Dos bombas estallaron el lunes causando la muerte de dos personas y heridas a otras 50, informó la Policía de Boston. (AP Foto/Josh Reynolds)

  • An armed FBI agent passes a Boston police officer following an explosion at the finish line of the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/Josh Reynolds)

  • A firefighter tends to an injured man following an explosion near the finish line of the Boston Marathon in Boston, Monday, April 15, 2013. (AP Photo/Michael Dwyer)

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  • In this photo provided by The Daily Free Press and Kenshin Okubo, people react to an explosion at the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/The Daily Free Press, Kenshin Okubo) MANDATORY CREDIT

  • Two people walk down the sidewalk as Boston police clear the area in Copley Square in the aftermath of two blasts which exploded near the finish line of the Boston Marathon in Boston Monday, April 15, 2013. The explosions Monday killed at least two people and injured dozens. (AP Photo/Elise Amendola)

  • This photo provided by Bruce Mendelsohn shows the scene after two explosions occurred during the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/ Bruce Mendelsohn) MANDATORY CREDIT

  • Medical workers respond following an explosion at the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/The Boston Globe, David L Ryan) MANDATORY CREDIT

  • Boston police direct runners who were diverted from the race course following an explosion at the finish line of the Boston Marathon in Boston, Monday, April 15, 2013. (AP Photo/Michael Dwyer)

  • Medical workers aid injured people at the finish line of the 2013 Boston Marathon following an explosion in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/The Boston Globe, David L Ryan) MANDATORY CREDIT

  • Medical workers aid injured people at the 2013 Boston Marathon following an explosion in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/The Boston Globe, David L Ryan) MANDATORY CREDIT

  • Blood from victims covers the sidewalk on Boylston Street, at the site of an explosion during the 2013 Boston Marathon in Boston, Monday, April 15, 2013. At the right foreground is a folding chair with the design of an American flag on the cover. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/Charles Krupa)

  • Chris Darmody, right, holds his wife Sue in Boston, Monday, April 15, 2013. Chris says he was waiting for Sue when an explosion detonated near his location at the finish line of the Boston Marathon. The couple were later reunited after all runners were diverted from the course. (AP Photo/Michael Dwyer)

  • Emergency responders comfort a woman on a stretcher who was injured in a bomb blast near the finish line of the Boston Marathon Monday, April 15, 2013 in Boston. Two bombs exploded in the packed streets near the finish line of the marathon on Monday, killing at least two people and injuring more than 80, authorities said. (AP Photo/Jeremy Pavia)

  • Emergency responders aid a woman on a stretcher who was injured in a bomb blast near the finish line of the Boston Marathon Monday, April 15, 2013 in Boston. Two bombs exploded in the packed streets near the finish line of the marathon on Monday, killing at least two people and injuring more than 80, authorities said. (AP Photo/Jeremy Pavia)

  • Emergency responders comfort a woman on a stretcher who was injured in a bomb blast near the finish line of the Boston Marathon Monday, April 15, 2013 in Boston. Two bombs exploded in the packed streets near the finish line of the marathon on Monday, killing at least two people and injuring more than 80, authorities said. (AP Photo/Jeremy Pavia)

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  • In this image from video provided by Ryan Hoyme, the second explosion can be seen in the distance as smoke from the first explosion surrounds spectators exiting the stands during the Boston Marathon in Boston, Monday, April 15, 2013. (AP Photo/Ryan Hoyme)

  • knocked down runner

    Bill Iffrig, 78, lies on the ground as police officers react to a second explosion at the finish line of the Boston Marathon in Boston, Monday, April 15, 2013. Iffrig, of Lake Stevens, Wash., was running his third Boston Marathon and near the finish line when he was knocked down by one of two bomb blasts. (AP Photo/The Boston Globe, John Tlumacki)

  • A Boston Marathon runner leaves the course crying near Copley Square following an explosion at the finish line in Boston on Monday, April 15, 2013. (AP Photo/Winslow Townson)

  • People react as an explosion goes off near the finish line of the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions went off at the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/The Boston Globe, David L Ryan) MANDATORY CREDIT

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  • Multiple People Injured After Explosions Near Finish Line at Boston Marathon

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  • Boston police ask people to leave the area in Copley Plaza in the aftermath of two blasts which exploded near the finish line of the Boston Marathon in Boston Monday, April 15, 2013. (AP Photo/Elise Amendola)

  • Paramédicos asisten a un hombre herido después de una explosión en Boston el Lunes 15 de Abril de 2013. Dos bombas estallaron cerca de la línea de meta del maratón de Boston, causaron dos muertos y 22 heridos, dijeron la policía y los organizadores de la competición. (AP Foto/The Boston Globe, David L. Ryan)

  • Uniformed Division Secret Service officers stand watch on the sidewalk in front of the White House looking north from Pennsylvania Avenue during heightened security following the explosions in Boston, Monday, April 15, 2013 in Washington. (AP Photo/Charles Dharapak)