Iraqi police imposed a curfew to prevent an outbreak of violence in the southern Shiite city of Najaf Friday after a senior aide to cleric Moqtada Al-Sadr was shot dead. US aircraft killed 12 people in airstrikes overnight in strongholds of Sadr's masked Mehdi Army militia, who have been battling government and US troops for weeks. Police in Najaf set up road blocks and drove through the city with loudspeakers ordering shops closed and people off the streets, a Reuters reporter said, after Ryadh Al-Nuri, a top Sadr aide whose sister is married to the cleric's brother, was gunned down. Police and followers of Sadr in Najaf confirmed the shooting. It was unclear who had staged the attack. US and Iraqi forces have clashed repeatedly with Sadr's Mehdi Army since March, when Prime Minister Nuri Al-Maliki launched a crackdown on the militia in the southern city of Basra. Basra has been relatively quiet since Sadr called his fighters off the streets of Iraq's second largest city nearly two weeks ago. In the early morning hours of Friday, however, Iraqi troops were fired upon when they tried to enter the northern Basra district of Hayaniya, a Mehdi Army stronghold, police said. A US aircraft retaliated with an airstrike that killed six people and wounded one, a military spokesman said. “We had our eyes on an enemy mortar team which was firing on Iraqi armed forces on the ground,” said British Major Tom Holloway, spokesman for US and British forces in southern Iraq. “The mortar team had been engaging Iraqi ground forces.” US soldiers operating a drone plane over Sadr City, an eastern Baghdad Shiite slum, fired a Hellfire missile late on Thursday at a group of men carrying rocket-propelled grenade launchers, killing six, the US military said. Sadr City has been the focus of intense street battles over the past week that have killed close to 100 people. The slum is under a vehicle blockade, due to end Saturday, that has led to food and medicine shortages. __
