NAJAF, Iraq: Shiite radical leader Moqtada Sadr has ordered his followers not to launch any attacks on U.S. troops before the completion of their pullout from Iraq scheduled for by the end of the year.

"In order that Iraq can recover its independence through the withdrawal of the invaders from our territory, I judge it indispensable to halt all armed resistance operations until the complete withdrawal of the occupying forces," Sadr said in a statement received by AFP on Sunday.

"If the pullout is completed and there is no longer a single U.S. soldier on our territory, the military operations will end definitively but if that is not the case and Iraq remains in a state of dependency, they will resume with greater vigour," Sadr said.

He paid tribute to "the resistance for its actions" and said his movement was now working "hand in hand with the government to achieve the liberation of the country and supporting it against US pressure."

In July, Major General Jeffrey Buchanan, spokesman for U.S. forces in Iraq accused three Shiite militia groups of being behind attacks on U.S. troops.

He named them as the Promised Day Brigades, formed by Sadr in November 2008, and Kataeb Hezbollah and Assaib Ahl al-Haq, two splinter groups which broke away from Sadr's former Mehdi Army militia which fought US-led troops from 2004 to 2007.

The new U.S. Army chief warned on Thursday against leaving too large a force in Iraq after a year-end deadline, saying too many boots on the ground could feed the perception of an American "occupation."

General Ray Odierno commanded US forces in Iraq until last year and was one of the senior officers who spearheaded the troop "surge" in 2007, which the military believes turned the tide in the war and reduced sectarian violence.

He spoke amid a debate in Washington over the scale of a possible future U.S. military mission in Iraq and after Defence Secretary Leon Panetta endorsed a tentative plan for a force of 3,000-4,000 troops.

Some U.S. lawmakers have criticised that number of soldiers and say senior officers favour a larger force of at least 10,000, which would include a unit deployed in northern Iraq to defuse Arab-Kurdish tensions.

But Odierno told reporters the United States had to carefully balance how many troops were needed to assist Iraqi forces while scaling back the American profile in a country where anti-US sentiment still runs high.

"I will say when I was leaving Iraq a year ago, I always felt we had to be careful about leaving too many people in Iraq," said Odierno, who took over as army chief of staff on Wednesday.

"The larger the force that we leave behind ... [the more] comments of 'occupation force' remain," he added.