A parked car bomb exploded in a busy shopping street in predominantly Shiite eastern Baghdad on Saturday, killing at least four people and wounding 10, police said.

The bomb was the latest in a series of explosions targeting commercial centers.

The blast struck about noon, a peak time for street vendors and nearby stores along the Maaskar al-Rashid street, a popular gathering point for people selling tires and spare parts for automobiles. Police who gave the casualty toll said several stores also were damaged.

The attack came two days after explosions struck another Shiite market district in the Karradah neighborhood in central Baghdad as it was packed with shoppers, setting buildings and cars on fire and sending three huge columns of smoke billowing into the sky.

Interior Ministry spokesman Maj. Gen. Abdul-Karim Khalaf said the death toll in that attack had nearly doubled to 61 after more bodies were pulled from the rubble. He gave the number of wounded as 94.

He also provided a new explanation for the blasts, saying a single parked truck bombing had caused secondary explosions of two large generators and 10 nearby cars.

Iraqi police in the area said earlier that a garbage truck exploded near the market at about the same time as a Katyusha rocket slammed into a three-story residential building about 100 yards away.

Nobody claimed responsibility for either blast, but the market districts that dot Baghdad frequently have been targeted by suspected Sunni insurgents seeking to maximize the number of casualties in bombings despite a more than 5-month-old U.S.-Iraqi security crackdown.

Despite the unrelenting bombings, U.S. and Iraqi officials have claimed some success in reducing violence as they fight to gain control of the capital and surrounding areas ahead of a pivotal progress report to be delivered to the U.S. Congress in September.

But criticism has grown over failures of Iraq's leadership on the political front as parliament prepares to recess for an August vacation without passing key U.S.-backed legislation aimed at promoting national unity.

On Friday, Prime Minister Nouri al-Maliki's Shiite-dominated government denounced the country's largest Sunni Arab bloc for its threat to quit the ruling coalition, a move that would leave his Cabinet limping along with about a third of its members missing.

The National Accordance Front announced Wednesday it was suspending its membership in al-Maliki's government for now, but would quit it altogether if its demands were not met in a week's time. The 11 demands include a pardon for security detainees not charged with specific crimes, a firm commitment to human rights and the participation of all coalition partners in the handling of security issues.

Government spokesman Ali al-Dabbagh contended the criticism contained many "distortions" and amounted to an attempt to hinder the political process.

"The policy of threats, pressure and blackmail is useless," al-Dabbagh said in a four-page statement, which charged that the Front, which has six Cabinet members and 44 of parliament's 275 seats, has contributed to some of the policies it criticized.

Iraqi President Jalal Talabani, a Kurd, also called the move "unacceptable" and said in an interview with U.S.-funded Alhurra television that the Iraqi Accordance Front should have discussed its demands with the country's political leadership in private rather than publicizing them.

U.S. troops captured 16 suspected insurgents during raids targeting Al Qaeda in Iraq Saturday in raids in the northern cities of Samarra and Tarmiyah, the military said. The detainees included an alleged bombmaker who also was believed responsible for kidnappings, assassinations and extortion operations, according to a statement.

A fierce gunbattle broke out Friday after a joint U.S.-Iraqi force arrested a rogue Shiite militia leader in the holy city of Karbala, some 50 miles south of Baghdad, leading to an airstrike and the deaths of some 17 militants, the military said.

The military has promised to crack down on Shiite militias, which have been blamed for thousands of execution-style killings and roadside bombings, as well as on Sunni extremists usually blamed for suicide attacks and other bombings.