Baghdad, Iraq ? Shiite politicians failed to agree on a new prime minister Saturday, at least briefly delaying a key step in forming a new government nearly two months after national elections.

Elsewhere, a U.S. Marine helicopter fired two rockets into an insurgent hide-out in the western city of Ramadi, killing six militants, a Marine spokesman said. Two roadside bombs targeted U.S. troops in Samarra, injuring one American, the military said.

The 128 members of the Shiite alliance who won parliament seats in the Dec. 15 balloting gathered Saturday in Baghdad to choose a prime minister.

But the vote was postponed for at least a day at the request of the faction loyal to anti-U.S. cleric Muqtada al-Sadr because of differences with another group, according to Shiites who attended the meeting.

Shiite officials, speaking on condition of anonymity because of the sensitivity of the negotiations, said the al-Sadr faction was leaning toward Prime Minister Ibrahim al-Jaafari.

Another Shiite group had doubts about al-Jaafari, and al-Sadr’s lieutenants wanted time to confer, the officials said.

The disagreement could strengthen the position of the other major candidate: Vice President Adil Abdul-Mahdi. He is a French-educated former finance minister backed by the country’s top Shiite group.