A man wearing an Iraqi army uniform has shot dead two US soldiers and injured three others in a military base south of the northern city of Mosul.

The US army said the man was also killed in the incident but gave little information about the attack.

But Iraqi military reports said he was a soldier also working as an Imam at a mosque on the base.

No motive was given for the attack but Mosul is seen as the last remaining urban stronghold of al-Qaeda in Iraq.

The US army said it had received reports of "small arms fire" in Hamam al-Alil, 20 km (13 miles) south of Mosul.

"According to initial reports, an individual dressed in an Iraqi army uniform fired on the coalition forces and was killed in the incident," US military spokesman Major Derrick Cheng was quoted as saying by Reuters.

The mayor of the town, Saad Ali al-Jubouri, said US helicopters were hovering in the area and roads to the base had been sealed off.

The security situation has been improving in some parts of Iraq, but Mosul remains one of the country's most troubled areas with a strong Sunni insurgency.

Similar incidents involving attackers in uniform have happened in the past.

The US described an attack in February - in which an Iraqi policeman shot and killed a US soldier and an Iraqi translator - as "an anomaly".

The BBC's Natalya Antelava in Baghdad says the latest killings will add to concerns about militant infiltration in the security forces.