US carries out air strike in Iraq

A number of people have been killed in a US air strike in support of Iraqi forces fighting Shia militants in the town of Hilla, south of Baghdad.

US forces said four militants were killed, but Iraqi security sources have given casualty estimates ranging from 11 to up to 60 dead.

It comes after days of fighting sparked by an Iraqi crackdown on militias in the southern city of Basra.

The violence has spread to Baghdad and Kut, and more than 70 people have died.

Hundreds of people are said to have been injured.

Helicopter strike

A US forces spokeswoman, Major Allayne Conway, said US helicopters had responded to a call for help from special police units in Hilla on Wednesday.

"The Hilla SWAT guys were on the ground. They were engaged. Our attack helicopters were called in. They engaged," she said.

The four dead were said to be "special group criminals", a term the US military uses to refer to breakaway cells of the radical Shia militia, the Mehdi army.

The head of the Mehdi army, radical Shia cleric Moqtada Sadr, has spoken of the possibility of negotiations to end the violence.

On Wednesday, Iraqi Prime Minister Nouri Maliki gave Shia militants in Basra 72 hours to lay down their arms or face "severe penalties".