A homicide bombing at a Shiite (search) mosque Sunday in this eastern city killed four people, including two security guards who lost their lives confronting the attacker and preventing a far greater number of deaths.

About 70 to 80 people were inside the mosque for Sunday evening prayers when a man carrying a briefcase tried to enter but was blocked by the security guards, officials said. A bomb in the briefcase exploded after a scuffle, during which one of the guards opened fire.

"Our two security guards were martyred and the suicide bomber was killed," said witness Sajjad Bhutta. The other dead man was a passer-by.

Punjab province Law Minister Raja Basharat Illahi said four people, including the bomber, were killed at the Husainia Hall mosque during prayers. Eight others were wounded.

Meanwhile, thousands of people mourned two Sunni Muslim (search) clerics who were gunned down in Karachi on Saturday, and authorities rounded up scores of people with links to militant groups to forestall more attacks.

The mosque bombing was the third this month against a religious target in Punjab in apparent rising strife between Shiite and Sunni Muslims.

On Oct. 1, a homicide bombing at a Shiite mosque killed 31 people in Sialkot city, then six days later, a car bombing at a gathering of Sunni radicals in Multan city killed 40 people.

No group claimed responsibility for those attacks, which prompted authorities to ban religious gatherings nationwide except for Friday prayers at mosques. It was not clear why prayers were held Sunday night.

An intelligence official said Sunday that more than 125 Pakistanis with links to outlawed extremist groups were detained for questioning over the weekend in connection with the Sialkot and Multan bombings.

They were picked up in raids on homes, mosques and Islamic seminaries in cities including Multan, Jhang, Lahore and Rawalpindi, the official said, speaking on condition of anonymity. None was a senior militant leader, the Multan-based official said.

Adding to the tensions, on Saturday two prominent Sunni clerics, Mufti Jamil and Nazir Ahmed Taunsvi, were gunned down in the volatile southern city of Karachi, triggering nighttime riots by their followers who set fire to at least four vehicles.

On Sunday, some 10,000 mourners gathered at a downtown Islamic seminary, where funeral prayers for Jamil were held amid tight security, with police sharpshooters on rooftops and riot police deployed outside gas stations and banks. A few hundred youths threw stones at police who fired tear gas and a few shots in the air to disperse them.

Jamil was known as a pro-Taliban scholar. He was part of a delegation that traveled to Afghanistan after the Sept. 11, 2001, attacks in America to try and persuade Taliban leaders to hand over Osama bin Laden.

The spate of attacks in Pakistan over the past 10 days comes despite scores of arrests of terror suspects in recent months, and the Sept. 26 killing by security forces of key al-Qaida suspect, Amjad Hussain Farooqi — accused in the 2002 beheading of American journalist Daniel Pearl and allegedly a recruiter for the terror network in Pakistan.