Police have imposed a curfew in the Iraqi city of Najaf after a senior aide to Muqtada al-Sadr, an Shia leader, was shot dead near his home, Iraqi officials said.

Riyadh al-Nouri, who was the director of al-Sadr's office in Najaf, was killed as he drove home from Friday prayers in the nearby city of Kufa.

Police set up blockades, ordered people off the streets and closed shops after the incident, a Reuters news agency reporter said.

Haider al-Turfi, another Sadr official in Njafa, said that armed men were waiting for al-Nouri near his home in the city's eastern neighborhood of al-Adala.

"When he arrived from the prayers, they opened fire on him, killing him instantly," Turfi said.

Al-Nouri's sister was married to Sadr's brother Murtada who was killed in 1999.

US 'responsible'

Dr Maha al-Duri, a representative of the Sadr bloc in Iraq's parliament, blamed the US military for the killing.

"This is one of the conspiracies contrived by the US occupation and their collaborators in Iraq against the al-Sadr movement," she told Al Jazeera.

"We strongly condemn the assassination of Sayyid Riyadh al-Nouri, one of the leaders of al-Sadr movement and hold the occupation forces responsible for the assassination."

Al-Duri demanded an investigation into the killing but reaffirmed that al-Sadr's followers were committed to maintaining the ceasefire with Iraqi forces.

"We have proved that we only have a national agenda, despite the continuation of the siege imposed on us," she said.

Along with Sheikh Mustafa al-Yacoubi, another al-Sadr loyalist, he was detained by American forces in April 2004 over the killing of Sheikh Abdul-Majid al-Khoei, a Shia cleric, in Najaf shortly after the US-led invasion.

Those arrests, along with the closing by US authorities of al-Sadr's newspaper, triggered an uprising that engulfed Shia areas of central and southern Iraq.

The two men were released in 2005.

Air raids

Al-Nouri's death came after fresh US air raids on Friday killed at least 12 people in Baghdad and Basra amid continued street battles between Shia fighters and Iraqi security forces in the two Iraqi cities.

Six fighters were killed by US aircraft in the southern port city of Basra, hours after a Hellfire missile fired from a drone killed six fighters in the capital, US and British military officials said.

The US military said an unmanned aircraft fired a Hellfire missile and killed six "heavily armed criminals" at around 9:45pm local time (1845 GMT) on Thursday.

It said the missile was fired after the drone observed a large group of people with rocket-propelled grenade launchers and mortar tubes.

Two previous air strikes announced by the military on Thursday killed six people in similar circumstances.

The strike in Basra happened when US aircraft hit an area in the northern al-Hayaniya district after identifying a group of fighters, Major Tom Holloway, the British spokesman, said.

Meanwhile, a rocket apparently aimed at the government and diplomatic Green Zone in Baghdad fell short, crashing into a second-floor room of the Palestine Hotel blowing a hole in the wall.

Basra crackdown

Basra was rocked by fierce clashes last month after Nuri al-Maliki, the Iraqi prime minister, ordered a crackdown on Shia armed groups, including al-Sadr's Mahdi Army.

Battles have raged since Sunday between Iraqi and US forces and Shia fighters from the Mahdi Army in eastern Baghdad's Sadr City.

Iraqi officials claim around 80 people have been killed, with scores wounded.

Al-Sadr's movement said on Thursday it was "under siege" in the district and warned that its militia was ready to take up arms again, breaking a ceasefire ordered by him last August.

PHOTO CAPTION

Family members and mourners raise the coffin with Riyadh al-Nouri, senior aide to radical Shiite cleric Muqtada al-Sadr, during the funeral march in the city of Najaf, 160 kilometers (100 miles) south of Baghdad, Iraq, Friday, April 11, 2008.

Al-Jazeera