Clashes between the Mahdi Army and US and Iraqi forces broke out in Sadr City in Baghdad late Friday after a senior aide to Muqtada al Sadr was murdered in the city of Najaf. US and Iraqi forces confirmed killing 13 Mahdi Army fighters in eastern Baghdad after a series of complex attacks.

The latest bout of fighting in the Mahdi Army strongholds in eastern Baghdad began after Riyad al Nouri was murdered by gunmen outside his home in Najaf. Nouri was in charge of Sadr's office in Najaf and was also Sadr's brother-in-law. Sadr immediately accused "the hands of the occupiers and their tails," referring to the Iraqi government, of conducting the attack. Prime Minister Nouri al Maliki immediately condemned the killing.

Iraqi security forces immediately clamped a curfew on the cities of Najaf and Hillah in an attempt to prevent retaliatory strikes from the Mahdi Army. The Mahdi Army suffered a setback during the six days of fighting at the end of March, and its capacity was degraded in the south-central cities of Najaf, Karbala, and Hillah. But Sadr still maintains influence in the region.

A series of clashes broke out in Sadr City in the late evening after Mahdi Army forces conducted several complex attacks against joint US and Iraqi patrols. The Mahdi Army used roadside bombs, rocket-propelled grenades, and sniper and small-arms fire from housing complexes in the city. One of the US and Iraqi convoys was transporting material to be used in the construction of a checkpoint that would be manned by the Iraqi Army.

Thirteen Mahdi Army fighters were confirmed killed in three separate engagements and "multiple others" are believed to have been killed. US forces used M1A2 Abrams tanks and Predator unmanned aerial vehicles to strike at Mahdi Army positions.

The Iraqi government had planned on lifting the curfew in Sadr City on April 12, but the recent fighting and the murder of Sadr’s brother-in-law has put the plan on hold.

Mahdi Army forces rose up after the Iraqi government started the assault on Basrah on March 25 to clear the city of the Mahdi Army and other Iranian-backed Shia militias. Sadr called for his forces to leave the streets on March 30 just as Iraqi Army and police reinforcements began to arrive in Basrah.

US and Iraqi forces killed 173 Mahdi Army fighters in Baghdad alone during the six days of fighting from March 25-30. The fighting has not abated in Sadr City and other Mahdi Army dominated neighborhoods in northern and eastern Baghdad.

Sadr and his political movement have become increasingly isolated since the fighting began in Basrah, Baghdad, and the South. The Iraqi government, with the support of the political parties, said the Sadrist political movement would not be able to participate in upcoming provincial elections if it failed to disband the Mahdi Army. Grand Ayatollah Ali al Sistani, the senior most Shia cleric in Iraq, said the Mahdi Army was not above the law and should be disarmed.