BAGHDAD, 24 December 2004 — The US military investigated how a suicide bomber managed to penetrate an army base in a strike that killed 24 people as three US Marines and a soldier were killed in two attacks in Iraq yesterday.

The Marines were killed while conducting security operations in the restive western Al-Anbar province, home to the former insurgency stronghold of Fallujah, where a few hundred residents entered the war-battered city for the first time since a massive US-led offensive against rebels in November.

In Baghdad, a roadside bomb claimed the life of a US soldier and wounded two others, while mortar attacks killed three civilians and one policeman. The fresh US military casualties came amid a major review of base security operations following Tuesday’s attack on an army dining hall in the northern city of Mosul. The US military’s second-in-command in Iraq, Lt. Gen. Thomas Metz, ordered a special investigation of how an infiltrator managed to penetrate the heavily guarded US military base.

“What’s going to happen is there will now be an ... investigation. Full force protection will be one of many areas looked at,” said spokesman Lt. Col. Steve Boylan. But he recognized the quandary of staving off attacks against US camps.

“It’s virtually impossible to have a 100 percent solution. We don’t have a force field around our bases,” he said.

Gen. Richard Myers, the chairman of the US Joint Chiefs of Staff, said Wednesday that the attack was probably the work of a suicide bomber.

The bomber was probably wearing an Iraqi Army uniform, US Brig. Gen. Carter Ham, commander of the Mosul base where the attack occurred, told CNN.

An Al-Qaeda-linked militant group, Ansar Al-Sunnah Army, which said it was a suicide bombing, claimed responsibility for the deadliest attack ever against the Americans in Iraq.

The strike was the second major bombing inside a citadel-like US base in two months after a double suicide blast in Baghdad’s Green Zone, home to the US Embassy and Iraqi government, that killed six in October. Mosul, the third largest Iraqi city, was once seen as relatively stable compared with the restive areas around Baghdad, but the situation has deteriorated over the last year.

Last month, the city burst into outright war between the Americans and insurgents when rebels overran police stations.

Meanwhile, a few hundred men returned to their homes in Fallujah yesterday, nervous about what they would find in the ghost town of rubble after six weeks of fighting between the US military and insurgents.

The men, some dressed in suits, others in leather jackets and tribal robes, showed their passports and tattered identity papers to US soldiers and Iraqi National Guard at a checkpoint.

— With input from agencies