KARACHI, Pakistan — Gunmen shot and killed two people returning from a funeral Monday for Shiite Muslim victims of a massive bombing in Karachi, highlighting escalating sectarian tensions in a city where 48 people were killed the day before.

The bomb exploded Sunday evening as people were leaving a mosque, and underlined the increasing threat Shiites face as Sunni militant groups target them in ever-bolder attacks. There was no immediate claim of responsibility but Sunni militant groups who do not consider Shiites to be true Muslims have carried out such attacks in the past.

Thousands of Shiite Muslims turned out Monday to bury their dead and demanded government protection from militant groups.

Some of those attending the funeral set fire to buses in one Karachi neighborhood as they went to the cemetery, said police official Qamar Ahmad.

When they moved through the same area after the funeral, gunmen opened fire on the group and wounded several protesters, he said. Two of the men died and 13 were wounded, said Dr. Saleem Memon, who works at the hospital where the wounded were taken.

The Sohrab Goth neighborhood where the shooting occurred is home to many ethnic Pashtuns who traditionally live in northwestern Pakistan and eastern Afghanistan.

Over the years, many have migrated to the port city of Karachi. Security officials in Karachi have raised concerns that members of the Taliban – also predominantly Pashtun – are taking advantage of the large Pashtun community to hide themselves in Karachi and establish a foothold there.

Dr. Jalil Qadir, a Pakistani surgeon, said 48 people were killed and at least 200 wounded in the Sunday attack.

Thousands of people thronged a main road in Karachi Monday for the funeral service. Many beat their chests and heads and chanted "Stop the brutal attacks!" They called on the government to take action against militant groups responsible for the attacks.

"Terrorists are killing us everywhere, but the state is nowhere to be seen," said Intizar Hussain, whose father died in the bombing.

It was the third mass casualty attack since the beginning of the year against Shiites. The first two killed nearly 200 people in the southwestern city of Quetta. Lashkar-e-Jhangvi, a Sunni militant group known for its virulent hatred of Shiite Muslims, claimed responsibility for the two attacks.

Last year was one of the most deadly for Shiites in the country's history. According to Human Rights Watch, more than 400 Shiite Muslims were killed across Pakistan in 2012. This year could be even more dangerous with nearly 250 Shiites already killed in the three attacks.

Pakistan's intelligence agencies helped nurture Sunni militant groups like Lashkar-e-Jhangvi in the 1980s and 1990s to counter a perceived threat from neighboring Iran, which is mostly Shiite. Pakistan banned Lashkar-e-Jhangvi in 2001, but the group continues to attack Shiites.

After the most recent attack in Quetta, the government launched a number of operations against the militant group and detained the founder of Lashkar-e-Jhangvi, Malik Ishaq.

In an apparent attempt to deflect criticism, Interior Minister Rehman Malik has repeatedly lashed out at government officials in Punjab province where the group is based and said they have failed to crack down on militant groups.

Prime Minister Raja Pervaiz Ashraf condemned the bombing late Sunday and ordered an inquiry into how the bombing was carried out. But many Pakistanis want more from the government.

"Go ask the sleeping government to wake up. Our brothers and sisters are dying every day. But the government is doing nothing," said Shagufta Rasheed, a Karachi resident.

The city shut down on Monday for a day of mourning to honor the dead. Markets, gas stations and transportation were closed as security officials patrolled the streets. At the site of the blast, family and friends looked through the rubble for missing family members.

"I am here to look for my relative," said Farzana Azfar. "People say he was here. But people say they have no idea about him."

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Associated Press writer Muhammed Farooq in Karachi contributed to this report.

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