BAGHDAD, Iraq (AP) _ A suicide car bomber shattered a relative lull in Baghdad's violence Monday, killing at least 28 people in a blast that touched off raging fires and a blizzard of bloodstained paper from a popular book market.
It was the largest bombing in the capital in three days, and came on the heels of a major push by nearly 1,200 U.S. and Iraqi troops into Sadr City, a Shiite militia stronghold and base for fighters loyal to radical cleric Muqtada al-Sadr.
Iraqi troops in Sadr City set up checkpoints and took a far more visible presence than Americans, who led the push into the area Sunday. The move was an apparent attempt to avoid Shiite anger in a place of past street battles with U.S. forces.
But pressure on al-Sadr and his Mahdi Army militia continued on other fronts.
In the southern city of Karbala, the home of a Mahdi Army leader was raided in a joint U.S.-Iraqi operation, the U.S. military said.
Al-Sadr's followers also warned the Iraqi government they would not relinquish Cabinet posts unless other members of the ruling coalition do the same _ setting the stage for a major political battle as Prime Minister Nouri al-Maliki prepares to reshuffle his administration.
Meanwhile, a British-Iraqi raid on a police intelligence headquarters in southern Iraq on Sunday found 30 prisoners with signs of torture and an alleged death squad leader was captured.
The raid took place at the National Iraqi Intelligence Agency building in Basra, Iraq's second-largest city 340 miles southeast of Baghdad. Inside, troops discovered the prisoners, including one woman and two children, with signs of torture and abuse, the British military said in a statement. It did not elaborate.
The Iraqi government criticized the raid and on Monday launched an investigation.
``We have a committee that ... has started work to uncover the circumstances of the incident,'' said Ali al-Dabbagh, a government spokesman.
Al-Maliki had ordered the inquiry a day earlier, and vowed to punish ``those who carried out this illegal and irresponsible act,'' his office said in condemning the raid. Al-Maliki's statement did not mention the prisoners.
On Monday, black smoke drifted over central Baghdad from burning shops, cars and book stalls in the mixed Sunni-Shiite area around Mutanabi street along the Tigris River. At least 66 people were wounded in the suicide blast, and the death toll could rise, police said.
``Papers from the book market were floating through the air like leaflets dropped from a plane,'' said Naeem al-Daraji, a Health Ministry worker who was driving about 200 yards from the blast and was slightly injured by broken glass from his car window.
``Pieces of flesh and the remains of books were scattered everywhere,'' he said.
People began driving the injured to hospitals in private cars without waiting for ambulances to arrive. A worker at a nearby shoe store, Youssef Haider, 24, said the blast flipped burning cars with charred bodies trapped inside. He and co-workers used two-wheel pushcarts used for shoe boxes to carry away the wounded.
Sporadic car bombs and attacks have hit the capital in recent days, but none with mass casualties since a blast Friday killed at least 10 people.
In other violence, gunmen opened fire on Shiite pilgrims in several places around Baghdad, killing at least seven people, police said. The Shiites were apparently heading to shrines and holy sites in southern Iraq for the annual commemoration of a 40-day mourning period for the death of a revered 7th-century warrior, Hussein.
The U.S. military said one American soldier was killed and another was wounded when a roadside bomb hit their convoy south of Tikrit. The Sunday night attack was under investigation, the military said in a statement. The names of both soldiers, who were assigned to the 13th Sustainment Command (Expeditionary) unit, were withheld pending family notification.
Meanwhile, Al-Maliki told The Associated Press on Saturday that he would reshuffle his Cabinet within two weeks, but did not say how many posts would be changed.
On Monday, an adviser to the prime minister said 10 ministers would be replaced. They include five of the six ministers loyal to al-Sadr. The adviser spoke on condition of anonymity because they were not supposed to release the information.
The Sunni bloc would lose two ministries and one deputy prime minister. The secular group led by former Prime Minister Ayad Allawi would give up two positions, the adviser said.
But the al-Sadr faction would take the biggest hit under the adviser's formula. Shiite ministers from other factions would remain in their jobs.
``We will not give up our share and any of our ministerial posts under any circumstances unless all other blocs are subjected to the same procedure,'' said Saleh al-Ukaili, head of Sadrist faction in parliament.
Al-Sadr's bloc also controls 30 of the 275 parliament seats.
South of Baghdad, a U.S.-Iraqi raid Sunday targeted rogue elements of al-Sadr's militia, the U.S. military said in a statement.
The military would not comment further, but a member of the Karbala provincial council, Hamid Kanoush, said his house was raided and his brother arrested. Kanoush also serves as a senior official in al-Sadr's political office in Karbala.
Five American helicopters hovered over his house as U.S. troops stormed inside, he said. They carried away his brother, Saad Kanoush, and destroyed furniture and pictures of al-Sadr.
Kanoush said he was not at home at the time, but that his family phoned him.
``I am a member of the provincial council and my activities are known by the public. If there a case against me, the Americans should have resorted to legal procedures, not terrorist acts against my family,'' Kanoush told The Associated Press.