BAGHDAD — A U.S. airstrike targeted a building in Baghdad's Sadr City on Thursday, hours after American soldiers clashed with Shiite militants in fighting that left 15 people dead, police and the U.S. military said.

The renewed violence coincided with the Congressional testimony of the Bush administration's top two officials in Iraq — Gen. David Petraeus and Ambassador Ryan Crocker. Petraeus recommended a pause in drawing down U.S. troops in Iraq while the security situation remains unstable and President Bush is expected to follow his recommendation.

But Prime Minister Nouri al-Maliki disagreed with Petraeus' proposal to delay further U.S. troop withdrawals, citing the growing capabilities of Iraq's own security forces.

Petraeus wants the U.S. to complete by the end of July the withdrawal of the 20,000 troops that were sent to Iraq last year, leaving about 140,000 in the country. Beyond that, the general proposed a 45-day evaluation period to be followed by an indefinite period of assessment before any further pullouts.

Al-Maliki, however, has said he disagrees with that decision.

The prime minister told Bush during a 20-minute telephone conversation on Wednesday that Iraqi security forces are capable of carrying out their duties and U.S. troops should be pulled out as the situation permits, according to a senior government adviser who sat in on the phone conversation. He spoke on condition of anonymity because he was not authorized to disclose the confidential details.

On Thursday, residents continued to flee fighting in the sprawling Sadr City district, which is home to some 2.5 million people.

Sadr City is a principal stronghold of the Mahdi Army militia of Shiite cleric Muqtada al-Sadr. Government troops supported by the U.S. military have been fighting to gain control of the area for the past 10 days.

Al-Maliki, also a Shiite, has faced widespread criticism over his decision to crackdown on the militias.

Violence in Iraq had declined last year and early this year following a cease-fire by al-Sadr, an influx of American troops and a Sunni revolt against al-Qaida in Iraq.

But the recent government crackdown on the Mahdi Army has provoked fierce retaliation, underscoring the fragility of the security gains.

A U.S. military statement Thursday said 13 militants were killed in four separate clashes during the night. It also announced the death of another U.S. soldier Wednesday in a roadside bombing in central Baghdad, raising to 18 the number of American troop deaths in Iraq since Sunday.

In one incident, the military said U.S. helicopters fired two Hellfire missiles on gunmen attacking troops and setting up concrete barriers at a checkpoint. Four of the attackers were killed, a statement said.

However, police said the four killed were civilians, including two brothers who were under 10 years old.

Police also said two more men were killed Thursday morning when a U.S. airstrike targeted a two-story building in Sadr City with missiles after a number of oxygen cylinders were spotted on the sidewalk outside.

The U.S. military said it was looking into the report. Local police in Sadr City have strong links to the Mahdi Army and frequently claim that civilians are killed in airstrikes targeting militants.

The fighting in Sadr City has taken a heavy toll on civilians, forcing hundreds to flee the sprawling district amid complaints of food shortages and fears of getting caught in the crossfire.

On Thursday morning, dozens of families squeezed through blast walls at the district's eastern entrance, carrying bags and pushing carts filled with clothes, groceries and other household items.

"We are fleeing because the shelling and airstrikes on us are increasing," said Nawal Abid, a homemaker dressed in a black robe.

The Baghdad military command announced that a two-week old vehicle ban in Sadr City would be lifted on Saturday, while a separate vehicle ban in another Shiite area of Shula would be lifted on Friday.

Associated Press writers Hamid Ahmed, Sinan Salaheddin and Qassim Abdul-Zahra contributed to this report.