Baghdad - Militants in Iraq on Friday killed the brother-in- law of radical Shiite cleric Moqtada al-Sadr in Najaf, some 180 kilometres south of Baghdad, Sadrist sources said.

Sources in al-Sadr's office told Deutsche Presse-Agentur dpa that Riyad al-Nuri, one of al-Sadr's closest aides, was killed by militants in front of his house north of Najaf.

Sources added that militants driving an identified vehicle targeted al-Nuri, who was married to al-Sadr's sister, after he had finished the Friday Muslim prayers.

Asmaa al-Mosawy, a member of the Sadrist movement, told dpa that the Iraqi forces were responsible for al-Nuri's death because the government has launched an offensive against all Sadrists since March 25.

"Al-Nuri's death is considered a severe loss to all Sadrists," al- Mosawy said.

She added, "He was an ideal model in obeying al-Sadr's orders".

Fatah al-Sheikh, another Sadrist, told dpa that al-Nuri had a leading personality and was respected by everyone.

He added that al-Sadr used to rely on him, as he significantly contributed to the current political situation.

"Al-Nuri's death aims at striking up strife," al-Shekih said, adding that al-Nuri was not an extremist, but a follower of al-Sadr's methods.

Reacting to the news of al-Nuri's death, the Iraqi forces imposed a curfew on the city of Najaf, especially in areas where Sadrists are centralized.

In other news, US airstrikes targeted houses in the Hussein district of Basra, some 550 kilometres south of Baghdad, killing one member of al-Sadr's Mahdi Army militia and wounding three civilians, witnesses said.

In another development, US helicopters continued Friday to attack the Sadr City area of east Baghdad, witnesses told dpa.

Loud explosions could be heard in the district, a stronghold of the Mahdi Army, which has been encircled by US and Iraqi troops since March 25.

Sadrist sources told dpa that joint US-Iraqi forces attacked the office of al-Sadr in the Nomaneiya area in the city of Kut, some 170 kilometres south of the Iraqi capital.

The troops burnt the office after killing the Sadrists inside it, the Sadrist sources said.(dpa)