Nine more American troops died in Iraq, the U.S. military reported Monday, five of them in a vehicle accident in a remote, rain-soaked western area. Their deaths brought the number of service members killed so far this month to 13 ¡ª nearly half the number who died in all of March.

An Iraqi wounded by a truck bomb are treated at a hospital in Sadr City Monday April 3, 2006 in Baghdad, Iraq. A truck bomb exploded Monday near the Shiite al-Shroofi mosque in northeastern Baghdad, killing at least 10 people and wounding 30 others, as worshippers left the mosque. [AP]

Three more Americans ¡ª two Marines and a sailor ¡ª were missing in the Sunday accident in which a truck overturned near Asad air base, a U.S. statement said. All the dead were Marines, the statement added.

It gave no reason for the accident except that it was not a result of hostile fire. Heavy rains fell over the area during the weekend.

Also Sunday, three Marines and a sailor were killed by "hostile fire" in Anbar province, which includes the Asad base, the military said. No further details, including the precise location, were released.

It was the first time that four American troops had been killed in a single attack since Feb. 22, when four soldiers of the 101st Airborne Division died in a bombing in northern Iraq.

Thirty-one U.S. troops died in Iraq in March, the lowest monthly death toll for U.S. forces since February 2004. But the relatively good news quickly became worse on the first day of April, when four troops were killed including two pilots who died when their Apache helicopter crashed.

U.S. officials said the helicopter was probably shot down. The militant al-Rashideen Army claimed responsibility, and Al-Jazeera television aired footage Monday provided by the insurgents which they claimed showed parts of the wreckage.

Although U.S. casualties have been on the decline, deaths among Iraqis have increased because of rising tensions between Shiite and Sunni Muslims. At least 1,038 Iraqi civilians died last month in war-related violence, according to an Associated Press count.

The AP count showed at least 375 Iraqi civilians killed in December, 608 in January and 741 in February. Most of the increase appeared a result of a sharp rise in the number of civilians found dead throughout Baghdad ¡ª apparent victims of sectarian reprisal killings.

The alarming rise in civilian toll has put new urgency into efforts by Iraqi politicians to form a new national unity government following the December elections. That message was delivered by Secretary of State Condoleezza Rice and British Foreign Secretary Jack Straw during a two-day visit that ended Monday.

"First and foremost, the purpose of this trip is to encourage and to urge the Iraqis to do what the Iraqis must do because the Iraqi people deserve it," Rice said. "But yes, the American people, the British people ... need to know that everything is being done to keep progress moving."

During their visit, Rice and Straw avoided any public call for Prime Minister Ibrahim al-Jaafari to step aside as the Shiite nominee for a second term ¡ª a key demand of Sunni and Kurdish politicians before they will join a new government.

Nevertheless, the visit clearly increased pressure on al-Jaafari, and for the first time officials of his own Shiite bloc called for him to step down.

Following the visit, al-Jaafari's supporters scrambled Monday to try to rally support for him, even as other politicians sought ways to remove him if he refused to step aside.

"We're waiting to hear the final position of the other blocs," al-Jaafari ally Ali al-Adeeb said. "Then we will study their position and decide. It is still to early for the (Shiites) to decide whether al-Jaafari's nomination should be withdrawn."

Al-Jaafari's critics accuse him of failing to curb the Sunni-dominated insurgency and calm tensions between Sunnis and Shiites. The Feb. 22 bombing of a Shiite shrine in Samarra triggered a wave of sectarian attacks that threaten to plunge the nation into civil war.

In the latest violence, at least 12 Iraqis were killed Monday in three vehicle bombings in mostly Shiite areas of the capital, police reported.

Ten of the victims died when a suicide driver detonated a truck filled with dates as worshippers were leaving the al-Shroofi mosque after evening prayers. Another 38 people were wounded, police and hospitals said.

Two others, including a 9-year-old boy, were killed in a car bombing in the Sadr City area. The third bomb exploded in the central district of Karradah, wounding six, police said.

Late Sunday, four Shiite civilians died when gunmen burst into their home in the religiously mixed Dora district of southwestern Baghdad. Police said the assailants lined up a brother, two sisters and an uncle against a wall and killed them.

The mother of the family was visiting relatives at the time. Police said the father, a grocery shop owner, had been killed six months earlier by gunmen in the same neighborhood.