A U.S. warplane strafed a house in a southern Iraqi city and killed eight civilians, including two women and one child, Iraqi police said Saturday.

The U.S. military had no immediate comment on the report, which came a day after the first American airstrikes were launched in Basra during a week-old offensive against militant followers of radical Shiite cleric Muqtada al-Sadr.

Seven other people were wounded when the plane fired on a house in Basra's Hananiyah neighborhood overnight, a local policeman said on condition of anonymity because of security concerns.

While the Iraqi police officer claimed it was a U.S. plane, British jets also have been providing air support in the area; it couldn't be immediately confirmed whether the plane was British or American.

The British military had no immediate information but said it also was looking into the reports.

"We are aware of reports of incidents in the Basra area resulting in civilian casualties," said Maj. Tom Holloway, a British military spokesman. "We are investigating those reports and do not have any further details at this time."

AP Television News footage showed smoke rising from Hananiyah. Pools of blood and a destroyed pickup truck were seen outside the home hit by the plane.

American support in Basra came as Iraqi troops struggled against strong resistance in the city, the nation's commercial center and headquarters of the vital oil industry. Clashes there have sparked retaliatory fights in Baghdad and other Shiite cities.

U.S. military intelligence analysis of the fighting in Basra indicated Iraqi security forces controlled less than a quarter of the city, CNN reported on Saturday, citing unnamed officials in the U.S. and Iraq. The analysis also said militia members have deeply infiltrated Basra's police units.

The fight for Basra is crucial for the government of Iraqi Prime Minister Nouri al-Maliki, who is staking his credibility on gaining control of the city, Iraq's second largest, which has essentially been held by armed groups for nearly three years. Al-Maliki flew to Basra earlier this week to personally assume command of the operation and has vowed there would be "no retreat."

The crackdown in Basra has provoked a violent reaction — especially from al-Sadr's Mahdi Army. His followers accuse rival Shiite parties in the government of trying to crush their movement before provincial elections this fall.

Their anger has led to a sharp increase in attacks against American troops in Shiite areas following months of relative calm after al-Sadr declared a unilateral cease-fire last August and recently extended it for six months.

In extracts of an interview broadcast by the Al-Jazeera television network, al-Sadr called Saturday for Arab leaders to voice their support for Iraq's "resistance" to what he calls foreign occupation.

Many Shiite militias, including the Mahdi Army, are believed to receive weapons, money and training from nearby Iran, the world's most populous Shiite nation.

The situation in Basra remained tense as a Friday deadline for gunmen to surrender their weapons and renounce violence expired, although a few complied. Al-Maliki's office announced a new deal, offering Basra residents unspecified monetary compensation if they turn over "heavy and medium-size weapons" by April 8.

In Baghdad, Iraqi police said U.S. helicopters carried out airstrikes on the Shiite neighborhood of Sadr City Friday night. Television footage showed destroyed buildings and the smoking wreckage of at least one car.

The U.S. military did not immediately respond to requests for information.

More than 50 civilians have been killed and 388 others injured in Sadr City since the U.S. and Iraqi forces began their crackdown, local hospital officials said on condition of anonymity for security reasons.

The U.S. military sharply disputes the claims, having said that most of those killed were militia members.

Some 40 policemen in Sadr City handed over their weapons to al-Sadr's local office, one of the policemen told The Associated Press on Saturday.

"We can't fight our brothers in the Mahdi Army, so we came here to submit our weapons," the policeman said on condition of anonymity for security reasons.

Sheik Salman al-Feraiji, al-Sadr's chief representative in Sadr City, said they gave the policemen olive branches and copies of the Quran.

Meanwhile, mortar or rockets were again lobbed on Saturday from Shiite areas in eastern Baghdad toward the Green Zone, the fortified area where the U.S. and British embassies are located, along with much of the Iraqi government. It wasn't immediately clear if the rounds hit the zone or landed nearby.