At least 58 US troops were injured in an apparent resistance attack on their base in the northern town of Mosul on Tuesday.
Elsewhere, three Iraqi Muslims are feared dead and several others, including three US troops, were wounded in an explosion that rocked a mosque in Baghdad, Aljazeera's correspondent reports.
In the Mosul attack, Major Trey Cate of the 101st Airborne Division said on Tuesday soldiers at the base in Tallafar, west of Mosul, fired on a vehicle when it failed to stop at an entry point. The vehicle then blew up.
Four soldiers with the worst injuries were transferred to the 21st combat support hospital in Mosul, 65km away.
According to Aljazeera's correspondent in Mosul, an Iraqi translator was among those injured. Tallafar is mainly populated by Shia Turkmen and has been calm since the US ousted president Saddam Hussein in April.
Elsewhere in the north, a US helicopter has come down 5km south of Falluja, Aljazeera’s correspondent reports.
The Tomahawk assault helicopter crashed in the suburb of Saddat al-Falluja on Tuesday afternoon.
Witnesses confirmed seeing the incident while others reported seeing flames coming from the aircraft.
The US military in Baghdad said the crash was a "controlled, hard landing" and there were no injuries or deaths from the incident.
An explosion that rocked a Sunni mosque in the Iraqi capital on Tuesday morning has now been described by the US military as a resistance car bomb attack.
Three worshippers died at the
Ahbab al-Mustafa mosque
Aljazeera's correspondent said three people were killed and several others injured in the blast after morning prayers at Ahbab al-Mustafa mosque in central Baghdad.
Asked if the bombing of the US compound was a human bomb attack, Major Cate said: "I'm going to have to assume that it was, as the individual was driving the car and it detonated."
He said only one person was inside. Three seriously wounded soldiers were flown to a combat support hospital in Baghdad, Cate said.
But local police have given a different account. "Unknown men planted a bomb in the courtyard" of Ahbab al-Mustafa mosque, one police officer said.
"We are pointing the finger of accusation at the Shia for this act," said Shaikh Ahmad Dabbash, who leads prayers at the damaged Ahbab al-Mustafa mosque, and linked the blast to previous attacks on Sunni mosques in the capital.
"Elements which claim to be Muslims, but which have nothing to do with Islam, came to divide Muslims and spread sectarianism in this country," he said.
An association of Iraq's Sunni clerics called the attacks part of a campaign against the Sunni sect, of which Saddam is a member and most of the people in areas where friction with US forces is highest.
"Sunni mosques and those who pray in them are being attacked... across Iraq by elements we know of, on a pretext we reject: that these are the supporters of the former regime," the League of Muslim Clerics in Iraq said in a statement.
"We are pointing the finger of accusation at the Shia for this act"
Shaikh Ahmad Dabbash,
Imam, Ahbab al-Mustafa mosque
Earlier, US military officials announced the deaths of three US soldiers in a road accident north of Baghdad.
The accident, which also left one wounded, occurred during a combat patrol northeast of al-Duluiyah on 8 December, said 4th Infantry Division spokesman Colonel Bill MacDonald.
"Two Striker infantry carrier vehicles were travelling on a rural road when the embankment collapsed causing them to roll over into a canal," he said.
Excluding deaths reported as accidental, 193 US soldiers have reportedly been killed in combat in Iraq since 1 May, when US President George Bush declared major hostilities over.