BAGHDAD, Iraq -- Efforts to form a unity government suffered a new setback Sunday as Iraqi leaders postponed a parliament session after failing to agree on a prime minister. Bombs targeted Shiites near a mosque and on a bus as attacks nationwide killed at least 35 people.

Four more Marines were reported killed in fighting west of Baghdad as the U.S. death toll for this month rose to 47 -- compared with 31 for all of March.

U.S. officials believe the best way to stem the violence is for the Iraqis to establish a government comprising Shiites, Sunnis and Kurds, paving the way for the United States to start withdrawing its 133,000 troops.

But progress has stalled over Sunni and Kurdish opposition to the Shiite choice of Prime Minister Ibrahim al-Jaafari to head the new government. With al-Jaafari refusing to step aside, acting speaker Adnan Pachachi called a parliament session for Monday, hoping the full legislature could agree on a new leadership after the politicians failed.

On the eve of the session, Pachachi announced a delay of "a few days" to give the religiously and ethnically based parties more time to agree on the new prime minister, president and five other top posts that require parliamentary approval.

Before the announcement, Shiite official Hussain al-Shahristani told Sunni and Kurdish leaders that his bloc, which controls 130 of the 275 parliament seats, would decide what to do about al-Jaafari "within the coming two days," Kurdish lawmaker Mahmoud Othman said.

Majority Shiites have been giving similar assurances for the past two weeks, and it was unclear how soon the issue could be settled.

Voters chose the new parliament on Dec. 15, but the legislature met briefly only once last month.

The bitter fight over al-Jaafari has heightened friction among the rival parties, raising the spectre of deadlock over other top jobs. Some Shiite officials say that if they must change their nominee for prime minister, other parties may not win approval of their first choices for major posts either.

Pressure has been mounting on the Shiites to replace al-Jaafari, whom critics accuse of failing to curb sectarian tension that has soared since the Feb. 22 bombing of a Shiite shrine in Samarra, which triggered a wave of reprisal attacks against Sunnis.

Shiite politicians not affiliated with major parties have proposed that al-Jaafari step aside in favor of another candidate from his Dawa party.

However, Dawa leaders complained of interference by outsiders and insisted they should decide al-Jaafari's fate, according to several Shiite officials who spoke on condition of anonymity because the negotiations were at a sensitive stage.

In an interview Sunday on CNN's "Late Edition," Iraq's ambassador to the U.S., Samir Sumaidaie, said Shiite lawmaker Ali al-Adeeb had emerged as a possible prime minister candidate. Al-Adeeb is a member of al-Jaafari's party but spent many years in Shiite-dominated Iran -- which could cause problems with the Sunnis.

Four Marines -- three from Regimental Combat Team Five and one from the 2/28 Brigade Combat Team -- died Saturday in Anbar province, the U.S. command said Sunday.

Their deaths raised to at least 2,376 the number of U.S. military members who have died since the war began in March 2003, according to an Associated Press count. The rise in U.S. casualties followed a sharp drop in March, which saw the lowest number of American dead in Iraq since February 2004.

At least 10 people died in a car bombing near a Shiite mosque in an outdoor market in Mahmoudiya, 20 miles south of Baghdad, police said. Three others were killed when a bomb exploded on a minibus in a Shiite area of eastern Baghdad, police said.

Earlier Sunday, six people were killed when U.S. troops stormed a house looking for an al-Qaida suspect in Youssifiyah, 12 miles south of Baghdad, the U.S. military said. Six people, including the suspect, were arrested. The military didn't identify the suspect but said he worked with foreign fighters to plan bombings.

In other developments, according to officials:

* Gunmen killed seven people in the northern city of Mosul as they drove from a police station where they had been working on renovations.

* A minibus north of Baqouba also came under fire and five passengers were killed, police reported.

* Two civilians were killed in an ambush south of Kirkuk.

* Two policemen died in an ambush near Baghdad's Sadr City area.

* Gunmen disguised as police commandos abducted 12 employees of a trading company in Baghdad.

* The bodies of three police recruits were found Sunday just west of Ramadi. Police said notes left on the bodies said: "This is the punishment for new police recruits."

-- Police discovered three corpses of handcuffed men in Baghdad -- two that were pulled from the Tigris River and a third that was found in a gutter in an eastern neighborhood.

-- Police found the body of an Iraqi soldier in Hillah.

-- In Najaf, Brig. Gen. Abbas Maadal said 29 policemen remain unaccounted for three days after their convoy was ambushed near the U.S. base at Taji just north of Baghdad. Nine police were killed in the attack Thursday night. Maadal said officials were trying to determine if the missing police were dead, captured or in hiding.