Fifty-eight American soldiers and at least three Iraqis have been hurt in northern Iraq in a suicide car bombing outside a US army base, the army says.
US forces in Mosul have suffered three attacks in three days
A spokesman for the 101st Airborne Division said the explosion happened at a base in Tal Afar, west of Mosul.
Soldiers guarding the base fired on a vehicle that had failed to stop, said spokesman Major Trey Cate.
A US helicopter, meanwhile, had to make an emergency landing after being fired on over Falluja, west of Baghdad.
"The helicopter was forced to make a hard landing - a
controlled landing," said US Central Command spokesman Major Peter J Mitchell.
Residents said the reconnaissance helicopter, from the 82nd Airborne Division, was hit by rocket-propelled grenade, the Associated Press news agency reported.
The two-man crew walked away from the aircraft uninjured.
Earlier, in Baghdad an explosion at a Sunni mosque reportedly left three people dead and two injured.
The explosion occurred shortly after dawn at the Ahbab al-Mustafa mosque in the city's western Hurriyah district.
Local police said a bomb exploded in the courtyard of the mosque after morning prayers.
The Mosul explosion happened at 0745 (0445 GMT) when a vehicle drove up to the gate of the base housing the 101st Airborne's 3rd Brigade.
It detonated after the troops opened fire.
Colonel Michael Linnington, the commander of the 3rd Brigade, said the attack was a suicide mission, adding that the attacker's remains were "all over the compound".
A large crater was left outside the gateway.
This was the third attack on soldiers from the 101st Airborne in the Mosul area in as many days.
On Monday, a US soldier guarding a petrol station was killed in a drive-by shooting and on Sunday another soldier died when a roadside bomb exploded, also injuring two others.
On Sunday, US General Ricardo Sanchez said he feared more attacks as Washington prepares to hand over power to Iraqis in the middle of next year.
"We expect to see an increase in violence as we move towards the transfer of sovereignty at the end of June," he said.
US troops in Iraq have been facing almost daily attacks by insurgents since Saddam Hussein's forces were defeated on the battlefield.
Almost 200 US soldiers have been killed since major operations were declared over on 1 May.
In a non-combat accident on Tuesday, three American soldiers died and one was injured when an embankment collapsed.
Their Striker infantry carrier vehicle crashed into a canal, while on patrol north of Baghdad.