09/10/2011 04:14 pm ET Updated Nov 10, 2011

Janet Napolitano On 9/11 Anniversary Terror Threat: 'Let's Go About Our Business'

NEW YORK -- Speaking at a conference for 9/11 victims' family members on Saturday, Homeland Security Secretary Janet Napolitano said New Yorkers should remain vigilant but not alter their daily routines in the face of a purported al Qaeda plot to strike the city on the tenth anniversary of the World Trade Center attacks.

"New York City, this city here, has some of the best and most robust law enforcement in the world, not just in the United States," Napolitano said.

"This weekend should be about commemoration and memory and perseverance and strength and resilience, and ... people should be aware of their surroundings," she said. "But like all New Yorkers, let's go about our business and do what we intended to do."

On Wednesday, intelligence officials received a tip that three terrorists, two of them perhaps U.S. citizens, might seek to explode a bomb in Washington or New York to mar Sunday's commemoration services. Since then, however, counterterrorism officials have struggled to find information backing up the tip. Even efforts to put a name on the terror suspects, if they exist, have proved elusive.

At the Voices of September 11th "Day of Remembrance" event, where she was the keynote speaker, Napolitano also told the crowd that there were "no guarantees" the United States wouldn't be struck by terrorists again at some point.

The country is "stronger and more prepared to confront the range of threats we face than we've ever been in our history, and yet we always have more that can be done," she said.