Baghdad - Prime Minister Nouri al-Maliki's coalition and another Shiite political bloc announced Tuesday night that they would band together to form a new government.

The agreement was widely seen as tenuous, however, because the factions have not settled on candidates for the premiership or other top jobs - sticking points that prevented the groups from running together in the March 7 parliamentary elections.

"We formed an alliance to form the biggest bloc in the next parliament," Ali al-Allaq, a leader in al-Maliki's State of Law coalition, said in an interview. "We agreed to postpone talking about the position of the prime minister until the next phase."

U.S. officials have expressed frustration over how slowly Iraqis have moved to form a government. The Americans fear the process could drag on for months, creating unrest that would coincide with the drawdown of U.S. troops currently underway.

Al-Maliki's State of Law won 89 seats in the next parliament. The other Shiite-dominated coalition, the Iraqi National Alliance, won 70. The Sunni-backed Iraqiya coalition won 91 seats. Iraqiya's leader, Ayad Allawi, a secular Shiite, contends that his group should get to form the next government because it received the largest number of seats.

If the alliance between the Shiite blocs holds, leaders would need to bring just a handful of other lawmakers into the fold to get the 163 votes required to appoint a new prime minister. The incoming parliament will have 325 members.

Such an alliance threatens to undermine U.S. interests in two ways. It could exacerbate a sense of marginalization among Sunnis, prompting them to once again resort to violence. And it could give anti-American cleric Moqtada al-Sadr's movement, the biggest vote-getter within the Iraqi National Alliance, a dominant role in the government.

The Sadrists have made clear they would like to control at least one of the ministries that oversee the army or police. U.S. officials fear that scenario because they consider the movement's armed wing, the Mahdi Army, a ruthless sectarian militia.

The main parties in the Iraqi National Alliance propelled al-Maliki to power in 2006, when he was seen as a malleable figure. Al-Maliki's relationship with his political allies soured during his years in power, most notably after he launched a crackdown on the Mahdi Army in spring 2008.

The alliance, whose leaders have close ties to Iran, was the largest bloc in the election that didn't put forward a possible contender for the premiership.

The announcement of the pact between the Shiite blocs came on the second day of a manual recount of ballots cast in Baghdad, which is being conducted at al-Maliki's request. He has alleged that ballots for his slate were undercounted because of human error and fraud. The recount is expected to last at least two weeks.

The outcome of the vote could also be altered by the disqualification of winning candidates for alleged ties to Saddam Hussein's outlawed Baath Party, an effort led by a government commission run by members of the Iraqi National Alliance.

- Special correspondents Jinan Hussein and K.I. Ibrahim contributed to this report.