Pakistani police launched an investigation to learn the identity of a homicide bomber who killed 15 people in an attack over the weekend on a Shiite mosque in the northwest city of Peshawar, officials said Sunday.

Meanwhile, the chief minister of North West Frontier Province, of which Peshawar is the capital, called for calm Sunday amid fears the bombing could spark a wave of sectarian violence between majority Sunnis and minority Shiite Muslims.

No group has claimed responsibility for Saturday's bombing in downtown Peshawar that also killed the city's police chief and wounded more than 30 other people, and came as Pakistan's Shiites began ceremonies in connection with their most important annual festival, Ashoura, which has often been a target of anti-Shiite violence.

Chief Minister Akram Durrani asked the general public to demonstrate "patience and maintain religious discipline," state-run Associated Press of Pakistan news agency reported.

Most Muslims from the majority Sunni and minority Shiite sects coexist peacefully in Pakistan, but militant groups on both sides are blamed for sectarian attacks that claim scores of lives every year.

Heavily armed police and security forces in pickup trucks and armored personnel carriers patrolled streets in Shiite-dominated areas in Peshawar on Sunday, but no violence was reported.

Investigators have collected human remains and bomb shrapnel from the scene of the bombing, said Fayyaz Toru, head of investigation department of Peshawar police.

Toru would not speculate on who might be behind Saturday's attack in Peshawar or a motive, only describing it as a "terrorist act."

Police have recovered two legs, without a torso, from the bombing scene and DNA tests will be performed on them to trace the identity of the body, Toru said Sunday.

Provincial police chief Sharif Virk said Sunday that the probe into the bombing was in the "initial stage" and it was impossible to link it with any militant group, Pakistan's Geo TV station reported.

Police have recovered fragments of wires that are believed to have been used in making the homicide bomb, Virk said.

Police also found remnants of a homicide belt with pieces of metal and a grenade, said another senior police officer on Saturday who requested anonymity because he was not authorized to talk about the investigation.

The blast went off in a bazaar area about 200 yards from a mosque that was the starting point for the Shiite procession, which was canceled. The blast caused a power outage that left the city center in darkness, complicating rescue efforts.

Most of the victims were police and municipal officials who were clearing the route for the Shiite procession, police said.

Although there was no immediate claim of responsibility, suspicion will likely fall on Sunni extremists, and an Islamabad-based analyst said that sectarian violence in Iraq was likely to add to Sunni-Shiite tension in Pakistan.

"I think it is going to reunite sectarian elements, who have targeted each others' worship places in the past," said Talat Masood, a political and defense analyst.

President Gen. Pervez Musharraf, a key U.S. ally in fighting Al Qaeda, condemned the "terrorist attack" and ordered an immediate inquiry, the state-run Associated Press of Pakistan reported.

The Sunni-Shiite schism over who was the true heir to Islam's Prophet Muhammad dates back to the seventh century. Shiites represent about 20 percent of Pakistan's Muslims, and Sunnis about 80 percent.

During the Shiite mourning rites processions are held in the lead up to Ashoura, the culmination of the mourning festival, where participants beat their chests, and some cut their backs with blades attached to chains in an expression of grief over the killing of Imam Hussain, prophet Muhammad's grandson.

Ashoura, the final day of the Shiite's mourning, will be on Tuesday.