A Pakistani surgeon says the death toll from a massive car bombing in the southern port city of Karachi has jumped from 37 to 45 as more victims died overnight.

Dr. Jalil Qadir says that 146 people were also wounded in the Sunday evening explosion. At least 32 of them are still in serious condition.

The blast targeted members of the minority Shia Muslim sect who were leaving a mosque when the bomb went off.

There was no immediate claim of responsibility but Sunni militant groups who do not consider Shia to be true Muslims have carried out such attacks in the past.

The city shut down on Monday for a day of mourning.

Demand for crackdown on violence

Thousands of people thronged a main road in Karachi Monday for a funeral service for 15 Shia 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 Shias. The first two killed nearly 200 people in the southwestern city of Quetta, which is home to many Hazaras — an ethnic group comprising mostly Shia Muslims who migrated from Afghanistan more than century ago.

Lashkar-e-Jhangvi, a Sunni militant group known for its virulent hatred of Shia Muslims, claimed responsibility for the two attacks.

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