BAGHDAD A group led by Al Qaeda in Iraq claimed responsibility on Tuesday for two suicide truck bomb that killed nine U.S. soldiers and wounded 20 in one of the worst attacks on U.S. ground forces since the invasion in 2003.
"Two knights from the Islamic State in Iraq ... driving two booby-trapped trucks hit the heart of the Crusader American headquarters in the region of Diyala," a statement from the Sunni group of the Islamic State in Iraq said in a Web posting.
In an interview to an Egyptian television station broadcast in Iraq on Tuesday, Prime Minister Nuri al-Maliki said Iraq had become the "most prominent arena in the fight against al Qaeda".
The U.S. military said on Tuesday night that two suicide trucks were involved in Monday's strike on a military outpost at Diyala, north of Baghdad, scene of fierce fighting between U.S. troops and Sunni Arab insurgents and al Qaeda militants.
It said in a statement one of the trucks exploded along an outer barrier, while the other blew up 30 metres from the base building. "The explosive blast from the second truck ruptured the wall of the patrol base building, collapsing the second floor and causing the majority of the soldier casualties".
It said nine soldiers were killed and 20 wounded. Most of the wounded later returned to duty.
Witnesses said the outpost was located in an old school in the village of al-Mukhisa.
"The building collapsed ... There was a huge fire," said one witness, who declined to be identified, describing the aftermath of the second truck bomb.
Near the city of Ramadi in western Anbar province, a suicide truck bomb killed 25 people and wounded 44, police said. They said the attack targeted police and civilians.
While frontal assaults by insurgents against heavily fortified U.S. bases in Iraq are rare, a two-month-old security plan that places troops in less protected garrisons in Baghdad and neighbouring regions has exposed them to greater risk.
The bombing of the outpost came as a showdown between President George W. Bush and Congress deepened over Democrat efforts to set a timetable for the withdrawal of nearly 160,000 troops.
Congress will vote this week on a funding bill that sets March 31, 2008, as the goal for pulling out most troops, but Bush repeated on Tuesday his vow to use his presidential veto.
FIGHTING FOR THE PROVINCE
Diyala, scene of Monday's attack, is a religiously mixed area where U.S. commanders last month sent a Stryker armoured force and 1,000 extra troops.
There has been a sharp upsurge in violence in the volatile province since the launch of a U.S.-Iraqi crackdown in Baghdad in February that forced Sunni Arab insurgents to regroup in areas outside the capital.
In the previous worst ground attack against U.S. forces in Iraq, 10 U.S. Marines were killed near Falluja, west of Baghdad, in a bombing on December 1, 2005.
The U.S. military also reported the deaths of two other U.S. soldiers on Monday.
At least 87 U.S. troops have been killed in Iraq this month, making April the deadliest since December, when 112 were killed.
At least 3,334 U.S. soldiers have been killed since the 2003 invasion that toppled Saddam Hussein.
On Tuesday, gunmen wearing uniforms of the Iraqi army raided a neighbourhood in Baquba, killing six people, wounding 15 and burning several homes, police said. A suicide car bomber on Monday killed 10 Iraqi policemen during a gathering of senior police officials in Baquba, including the city's police chief.
(Additional reporting by Richard Cowan in Washington)