Shiite cleric Muqtada al-Sadr will call on his fighters to maintain a cease-fire against American troops but may lift the order if a planned Iraq-U.S. security agreement lacks a timetable for the withdrawal of American forces, a spokesman said Thursday.

The statement by Sheik Salah al-Obeidi comes as al-Sadr plans to reveal details of a formula to reorganize his Mahdi Army militia by separating it into an unarmed cultural organization and elite fighting cells.

The announcement is expected during weekly Islamic prayer services on Friday.

Several cease-fires by al-Sadr have been key to a sharp decline in violence over the past year, but American officials still consider his militiamen a threat and have backed the Iraqi military in operations to try to oust them from their power bases in Baghdad and elsewhere in Iraq.

Al-Sadr's move appears to be an extension of plans he announced in June aimed at asserting more control over the militia by dividing it into a group of experienced members who would be exclusively authorized to fight and others who would focus on social, religious and community work.

But the cleric also apparently has decided to link the reorganization to ongoing U.S.-Iraqi negotiations over a long-term agreement that would extend the American presence in Iraq after a U.N. mandate expires at the end of the year. The White House's original goal was to have it completed by the end of July.

"This move is meant to offer an incentive for the foreign forces to withdraw," al-Obeidi said. "The special cells of fighters will not strike against foreign forces until the situation becomes clear vis-a-vis the Iraq-U.S. agreement on the presence of American forces here."

The new cultural group will be called Momahidoun, or "those who pave the way" in Arabic, in reference to the Mahdi, or so-called Hidden Imam, who disappeared as a child in the ninth century. Shiites believe he will return one day to bring justice to Earth.

It will replace the Mahdi Army, but elite cells of fighters will be created that could resume targeting U.S.-led foreign forces under strict guidelines, such as not harming Iraqis or infrastructure, said al-Obeidi, the al-Sadr spokesman.

The U.S. military cautiously welcomed the reorganization plan, saying it appeared to be an effort to help the Iraqi people. Residents in some Baghdad neighborhoods, however, said American troops were removing neighborhood fliers from al-Sadr's offices saying "a new organization will be established soon."

"The proof is always in the actions and not just the words," military spokesman Col. Jerry O'Hara said in an e-mailed statement.

Sporadic attacks have continued despite the cease-fires by al-Sadr, who is believed to be in Iran, raising questions about how much control he maintains over his militiamen. American commanders have consistently said they aren't targeting al-Sadr's followers but rather Iranian-backed breakaway factions.

Two U.S. soldiers were killed Monday by an armor-piercing roadside bomb known as an explosively formed penetrator, which the military believes is supplied by Iran to Shiite militia fighters. Iran denies it is supporting violence in Iraq.

On Thursday, a roadside bomb killed eight Bedouins, including three women and two children, on a remote desert highway west of Nasiriyah frequently used by U.S. and Iraqi troops, a police official said, speaking on condition of anonymity because he wasn't authorized to release the information.

Nasiriyah, about 200 miles southeast of Baghdad, is in a Shiite area that has been the site of fierce infighting between rival Shiite factions but has been relatively peaceful since a cease-fire declaration by al-Sadr.

Gunmen also killed a senior member of the Sunni Iraqi Islamic Party, Mahmoud Younis Fathi, and a colleague as they were driving to work in the northern city of Mosul, according to the group.

Elsewhere in Mosul, three Iraqi policemen were killed when a booby-trapped wooden cart exploded after they arrived to collect a body that had been left on the street beside it, police said.