Nine US soldiers have been killed in a suicide bomb attack on a base north of Baghdad, military officials have said.
The attack is the heaviest US ground loss for more than a year
Some 20 troops and an Iraqi civilian were injured in the attack, which happened in the volatile province of Diyala, to the north-east of Baghdad.
There has been fierce fighting in Diyala recently, pitting US and Iraqi forces against Sunni and Shia militias.
It is thought to be the worst single US loss on the ground since late 2005, when 10 marines died near Falluja.
In January 2007, 12 US soldiers died when a Black Hawk military helicopter crashed near Baghdad.
More than 3,300 US troops have been killed and some 24,300 have been injured in Iraq since the conflict began.
In Baghdad, meanwhile, two car bombs exploded on Tuesday morning near the Iranian embassy, police and witnesses said. At least four people were reported hurt in the blasts.
Two blasts in the same area on Monday left one person dead.
In a brief statement released early on Tuesday, the US military said a suicide car bomber attacked a patrol base near Baqouba, the capital of Diyala province, on Monday.
MAJOR US LOSSES IN IRAQ
2 Nov 03: Chinook helicopter downed near Falluja, killing 16
15 Nov 03: Two Black Hawk helicopters collide avoiding ground fire in Mosul, killing 17
21 Dec 04: Suicide bomb at military base in Mosul kills 19
26 Jan 05: CH-53E helicopter crashes in West Iraq, killing 31
3 Aug 05: Roadside blast near Haditha kills 14 marines
1 Dec 05: Ten marines killed by roadside bomb near Falluja
20 Jan 07: Black Hawk crashes near Tal Afar, killing 12
24 Apr 07: Suicide bombing of base near Baqouba kills nine
Fifteen of the wounded soldiers were later able to return to work, the statement said.
American troops in the province come under frequent mortar and small arms attack, but a frontal assault like this on a base is rare, says the BBC's Andrew North in Baghdad.
Most are now too well defended for suicide attackers to get close. But the base that was attacked is a smaller installation and so may have been more vulnerable, our correspondent adds.
The US military also announced the death on Monday of another soldier in a separate roadside bombing in Diyala.
The suicide bombing at the US base came at the end of a day of attacks across Iraq that left more than 40 people dead.
Car blasts in the town of Ramadi killed 20 people and injured many more. Three car bombs exploded in quick succession near a restaurant and market in Ramadi's western district of al-Taamim.
Earlier in the day, at least 20 people died in separate car bombings in Baqouba and Mosul.
Another attack took place on the edge of Baghdad's fortified Green Zone, close to where the new US envoy, Ryan Crocker, was giving his first briefing in Baghdad.
In a news conference, Ambassador Crocker said the next few months would be critical in the effort to reconcile Iraq's warring communities and urged the government to make use of a US-led security plan in the capital.
He also defended the thinking behind a controversial wall being built around the flashpoint Adhamiya area, a Sunni enclave on the mainly Shia east bank of the Tigris.
On Sunday Iraqi Prime Minister Nouri Maliki said he had ordered a halt to the project after it drew strong criticism from residents and Sunni leaders.
The latest US deaths also came as Democratic Party lawmakers in the US Congress agreed to merge House and Senate versions of a spending bill for Iraq, which include a timeline for the withdrawal of US troops.
The bill calls for a withdrawal to start no later than 1 October 2007, with a non-binding deadline of 31 March for a total pullout.
On Tuesday, US President George W Bush repeated his promise to veto the bill.