A suicide car bomber struck a US military oustpost north of Baghdad, killing nine soldiers and wounding 20 others, in the deadliest attack on American forces in 16 months.
The bomber exploded his explosives-laden vehicle against a patrol base in the restive province of Diyala on Monday and brought the US military death toll for April so far to 70, according to the US military.
Fifteen of the wounded were later able to resume their duties, but the attack was still the bloodiest since December 1, 2005 when 10 US marines are killed and 11 wounded by a roadside bomb on the outskirts of Fallujah.
It came as Diyala province emerges as one of the fiercest battle grounds in Iraq.
Another US soldier was killed by a roadside bombs the Diyala town of Muqdadiyah on the same day, according to his command.
The latest fatalities took the military's losses in Iraq to 3,330 since their March 2003 invasion, according to a count based on Pentagon figures.
A British soldier was also killed in the southern city of Basra, taking to 145 the number of British troops who have died in Iraq since 2003.
Monday was also a deadly day for Iraqi police and civilians, with at least 27 killed and dozens wounded in attacks across the country.
Here again, Diyala province saw much of the carnage.
In Diyala's capital, Baquba, another suicide car bomber attacked a police patrol near the provincial council headquarters as representatives gathered for a budget meeting, killing seven police and wounding 12 more.
"This will not deter the work of the honourable and dedicated to bring about security, peace and prosperity," said Diyala's Governor Raad Hameed Al-Mula Jowad Al-Tamimi, and the meeting went ahead as planned.
The bomber exploded against a police patrol that was directing traffic to allow a US convoy to pass, and it was not clear what the target was.
Fighting has intensified in the palm groves and market towns of Diyala, already a battle ground between Sunni insurgents and Shiite militia, since February 14 when US and Iraqi forces launched the Baghdad security plan.
In the capital itself, the plan has seen a "surge" in troop numbers as new US commander General David Petraeus attempts to quell sectarian infighting long enough to allow Prime Minister Nuri al-Maliki's government space to rule.
Despite this, and amid mounting US casualties, car bomb attacks have continued to target Shiite civilians.
The new US ambassador in Iraq, Ryan Crocker, used his first press conference on Monday to urge Iraqi politicians seek national reconciliation.
"I think the Baghdad Security Plan led by Iraq, supported by the coalition, can buy time, but what it does is buy time for what ultimately has to be a set of political understandings among Iraqis," he told reporters.
"These months ahead are going to be critical as this plan continues forward to increase security and gain the time, but most especially as Iraqis then try and use that time to grapple with some of these difficult issues," he said.
Meanwhile, US President George W. Bush said he would oppose any effort to set a timetable for a US withdrawal from Iraq and said that a US-led security crackdown had reduced sectarian violence there.
"There's been some progress. There's been some horrific bombings, of course, but there's also a decline in sectarian violence," Bush said as he met in the Oval Office with Petraeus.
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