At least 11 people have been killed and 20 injured in clashes between US troops and militiamen in Baghdad's Sadr City.

The fighting took place just hours after the signing of a ceasefire deal, agreed between the Iraqi government and Shia cleric Moqtada Sadr.

Police and medical sources confirmed the number of casualties, but the US military only identified three gunmen killed by troops.

It was unclear whether the others killed were militiamen or civilians.

The clashes came as as the US military was completing the building of a barrier designed, the military says, to isolate members of the Mehdi Army from the southern part of Sadr City.

Missile strike

A spokesman for US forces said troops had responded to several attacks by militiamen with precision strikes.

Two fighters, he said, were killed in a Hellfire missile strike by an attack aircraft, while they were planting a bomb targeting security forces.

A third man was shot dead as he tried to set up another road bomb, and other attacks were suppressed with tanks and attack aircraft.

Hospital sources said the dead included women and children.

On Saturday, Iraq's ruling alliance and Moqtada Sadr's opposition movement agreed to end seven weeks of fighting in Sadr City, though both sides said it would be Wednesday before the agreement is fully implemented.

Lt Col Steven Stover blamed what he called "special groups" for provoking Monday's clashes, saying: "They are obviously not listening to any agreement."

Tens of thousands of gunmen profess allegiance to Moqtada Sadr and his Mehdi army, but it is unclear how much influence he has over them, and over splinter groups.

The fighting in Sadr City followed the launching of a government crackdown on Shia militias in the southern city of Basra in late March.

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