The Karachi police chief was fired Wednesday, and the government promised more changes after three days of unrest that has left at least 26 people dead and brought Pakistan's largest city to a standstill.

Government officials struggled to explain what was behind the wave of violence, with one accusing Al Qaeda of trying to spark sectarian fighting between the Sunni Muslim majority and the Shiite minority.

The chief minister of Sindh province, Ali Muhammad Maher, met with security chiefs to discuss the worsening situation in the city of 14 million people, triggered by the assassination of a prominent Sunni cleric Sunday and the suicide bombing of a Shiite mosque a day later.

The death toll in the mosque attack rose to 21 on Wednesday, after a 30-year-old man died of his injuries. No one has claimed responsibility for either attack.

Rioting by Sunni and Shiite mobs followed the attacks, with most violence — including gunfire — aimed at hundreds of riot police deployed in different neighborhoods. Shops, cars, buses and government buildings were set afire. Four people, all civilians, died in exchanges of gunfire.

Karachi police chief Asad Malik and two other senior officers were transferred Wednesday, police spokesman Mughis Pirzada said. No explanation was given and no replacements announced.

"We cannot leave Karachi to the mercy of terrorists and we cannot afford any negligence when the lives and property of people are involved," Maher said. "The police have to work to control the situation and bring Karachi back to normal."

Information Minister Sheikh Rashid Ahmed promised more "administrative changes" in Sindh province and its capital Karachi within 10 days.

Police closed roads and took positions outside the U.S. Consulate, a frequent target of terrorist attack in recent years, after a Shiite group announced plans to demonstrate there. But by late Wednesday, no protesters had turned up.

The rioters have vented anger at U.S. interests, with mobs chanting "Death to America" and burning KFC and McDonalds restaurants. Anti-U.S. feeling grew in Pakistan after President Gen. Pervez Musharraf (search) allied the country with Washington in the war on terror after Sept. 11, 2001.

Karachi is a flashpoint for Pakistan's religious and ethnic divisions and the city has a history of Sunni-Shiite conflict. The metropolis had been showing signs of calm in recent months until a bombing at Shiite mosque May 7 that killed 22 people.

That bombing was followed by violence during by-elections that left 10 dead and the twin car-bombing a week ago near the residence of the U.S. Consul-General that killed a policeman and wounded 40 others.

Religious Affairs Minister Ijazul Haq told a news conference in the capital, Islamabad, that the most recent violence was "Al Qaeda related."

"There are no Sunni fighting Shiites," Haq said. "There is no sectarian fighting. But the whole purpose behind this is that there should be a Shiite-Sunni clash. This is a very well-calculated strategy, which is being implemented by terrorists."

Earlier, Abdur Rauf Chaudhry, an Interior Ministry spokesman, refused to speculate on an Al Qaeda role and said, "We think they were sectarian incidents."

Only scattered violence was reported Wednesday, with groups of youths throwing stones in some places and one vehicle set afire. Shopkeepers closed their shutters and many workers stayed home to protect their lives and vehicles.

Police freed about 60 of the 150 people they had detained during the previous three days and kept up heavy patrols.

An Islamic fundamentalist religious grouping, Mutahida Majlis-e-Amal (search), called for a strike in Islamabad on Friday to protest the violence and accused unnamed "enemy agents" of killing both Sunnis and Shiites to break "sectarian unity."

About 80 percent of Pakistan's 150 million people are Sunni Muslims, about 17 percent Shiites, and the rest Christians and other minorities.