Shiite Muslims in the southern Pakistani city of Karachi demanded government protection Monday from a wave of violence that has targeted the minority sect, a day after a massive bombing in the city killed 45 people.

The bomb exploded on Sunday evening as people were leaving a mosque in this port city, 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.

At least 146 people were also wounded in the explosion and 32 of them remain in serious condition, said Dr. Jalil Qadir, a Pakistani surgeon.

Thousands of people thronged a main road in Karachi Monday for a funeral service for 15 Shiite Muslims killed in the attack. 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, which is home to many Hazaras _ an ethnic group comprising mostly Shiite Muslims who migrated from Afghanistan more than century ago.

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 in targeted attacks across Pakistan in 2012. This year could turn out to 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 that they had failed to crack down on militant groups in the province.

Prime Minister Raja Pervaiz Ashraf condemned the bombing late Sunday and ordered an inquiry into how the bombing was carried out. But for many Pakistanis, these phrases ring hollow after so many attacks.

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

Karachi 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 family members missing since the explosion.

"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. It appears that some bodies are still in the rubble."

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