Sunday's heaviest fighting in weeks came on a day when militiamen blasted Baghdad's heavily fortified Green Zone with rockets and mortars, taking advantage of a blinding dust storm that grounded US attack helicopters.

The biggest clash in the day-long battles came at dusk Sunday when "a large group of criminals engaging with small-arms fire" attacked a security force checkpoint, a US military statement said.

"US soldiers used 120 mm fire from M1A12 Abrams tanks and small-arms fire to kill ... 22 criminals, forcing remaining enemy forces present to retreat," the military said.

"The criminals' small-arms fire was ineffective and there were no US soldier or Iraqi security force casualties in the attack."

At about the same time, seven fighters who ambushed a patrol were killed by US troops. Other gunmen died in various skirmishes during the day when troops retaliated after being attacked with small-arms fire and rocket-propelled grenades, the military said.

Most of the fighting took place in Sadr City, the Baghdad bastion of the Mahdi Army militia of radical Shiite cleric Moqtada al-Sadr, who claim they are being deliberately targeted.

US and Iraqi commanders say they are trying to halt rocket attacks from Sadr City on the Green Zone, where the Iraqi government and US embassy are based, by Iranian-backed militiamen using Iranian-supplied weaponry.

Tehran strongly denies any involvement.

The Green Zone was hit by waves of rockets and mortar rounds on Sunday evening, but there were no immediate reports of casualties.

With no US warplanes flying due to the dust storm, militiamen were able to launch their attacks without being targeted from the air.

Sadr City is a bastion of the Mahdi Army militia of radical Shiite cleric Moqtada al-Sadr
©AFP - Ahmad al-RubayeThe latest deaths bring to around 440 the number of militiamen and civilians killed in a month of clashes in Sadr City, where violence erupted after Prime Minister Nuri al-Maliki ordered a countrywide crackdown on militias on March 25, starting in the southern oil city of Basra.

At least 15 US soldiers have died in Baghdad since the clashes began.

Sadr's office in the shrine city of Najaf said new efforts were being brokered by President Jalal Talabani to try "to end the crisis between the Sadr movement and the government."

The meeting would see Talabani acting as mediator between government and Sadrist representatives, according to Sadr's spokesman in Najaf, Salah al-Obeidi.

"We are looking for assurances that the government will commit itself to the agreements. The government reneged on its commitments under the previous agreement," Obeidi told AFP.

He was referring to a deal struck late last month under which Sadr agreed to call his fighters off the streets in return for the government ending random raids and military assaults on Mahdi Army fighters.

"The involvement of President Jalal Talabani is guarantee that the government will respect the agreements," Obeidi said.

Sadr's group rejected Maliki's conditions for an end to the fighting late on Sunday.

"He (Maliki) is saying that the government has the right to do whatever it wants. We say the crisis can be resolved by objective dialogue," Obeidi said.

Maliki laid down four conditions for an end to the military onslaught against the Mahdi Army in an interview with Al-Arabiya television on Saturday.

These were that all heavy and medium weapons be handed in, that there be no further interference in the work of government departments or the police and army, and that wanted suspects be turned in.