Angry Shias ransacked several shops and hurled stones near the mosque hit in Monday's bombing, as a huge funeral procession descended into violence along a major highway in the southern city of Karachi. Hundreds of police fired tear gas at the crowd.

Fearing sectarian clashes between rival Shia and Sunni Muslims, thousands of police and paramilitary rangers were on maximum alert, and were also equipped with live ammunition, although there were no reports of firing at the procession.

President Gen. Pervez Musharraf pledged action to stem the wave of bloodletting. The bombing ripped through Imam Bargah Ali Raza mosque during evening prayers on Monday, also injuring at least 42 people, police said.

The attack sparked nighttime rioting by hundreds of enraged Shia youths who burned shops, cars, a bank and a government building and blocked highways and the main rail line. A shootout between rioters and police left three more people dead.

No one claimed responsibility for the bombing. But Karachi has been wracked by violence between the Sunni Muslim majority and Shia minority, and the attack was seen as revenge for the assassination Sunday of a senior Sunni Muslim cleric, Nazamuddin Shamzai, that also triggered street battles between youths and police.

"Apparently, it was a suicide attack," Manzoor Mughal, a senior police investigator, told The Associated Press following night-long operations to recover bodies and sift through the rubble. "We did not see any crater in the mosque, which shows that it was a suicide attack."

Karachi police chief Asad Ashraf Malik said a body retrieved from the scene was being examined to determine whether it was that of a suicide bomber.

The death toll rose to 19 Tuesday when three of the injured died of their wounds.

Musharraf expressed grief over the killings and promised to take an "important step" in response, Information Minister Sheikh Rashid Ahmed quoted him as saying.