Sadr's statement, issued Friday, seemed aimed at increasing pressure on the Iraqi government, which under a draft agreement of the SOFA doesn't envision complete withdrawal of U.S. troops until 2011, The Washington Post reported.

Sadr's Mehdi Army has largely been observing a cease-fire since last spring after battling U.S. troops since 2004. In his statement, which was read on his behalf at Friday prayers in Baghdad's Sadr City and in the city of Kufa, he reiterated a demand that U.S. troops leave Iraq "without establishing any bases or signing the agreement."

Sadr said if U.S. forces stay in Iraq, he would "support the insurgents," and added, "Our weapons would be aimed only against the occupiers, wherever they are" and not against Iraqis, the Post reported.

Iraq Prime Minister Nouri al-Maliki, a Shiite, has not said whether he supports the draft SOFA, which is meant to provide legal underpinning to the U.S. presence in Iraq after a mandate set by the United Nations expires Dec. 31.