A statement by the US command at the Prince Sultan Airbase in Saudi Arabia said "coalition aircraft may have engaged special operations and friendly Kurdish ground forces approximately 30 miles southeast of Mosul."

"Coalition aircraft were conducting close air support missions at the time (around 0915 GMT), and were in coordination with ground forces. The circumstances contributing to the incident are under investigation and unknown at this time."

The US statement offered no casualty toll but hospital sources in Arbil said four Americans were among the dead, while Kurdistan Democratic Party (KDP) external relations official Hoshyar Zebari said 12 Kurdish peshmerga fighters were killed and 44 wounded.

"There was (Iraqi) firing and the American special forces asked for close air support, but unfortunately two aircraft bombed the joint forces," Zebari said.

Among the seriously wounded was Wajih Barzani, 33, the head of KDP special forces and brother of party leader Massoud Barzani, he said.

"This is just a scene from hell here. There are vehicles on fire, bodies lying around, and there are bits of bodies around me," the BBC's world affairs editor John Simpson said on air.

"They hit their own people. They've killed a lot of ordinary characters. I'm just looking at the bodies now and it's not a very pretty sight," Simpson said, calling it "a really bad own goal by the Americans."

If the details of the attack are confirmed it would be the worst "friendly fire" incident in the 18-day-old US-British war on Iraq, which has already seen several deadly encounters between coalition troops.

Prior to Sunday's incident, investigators from US Central Command's forward planning base had confirmed one US death from friendly fire, which occured earlier this month when a US serviceman mistaken for an Iraqi soldier was shot dead by his own troops in central Iraq as he was investigating a destroyed Iraqi tank.

Central Command officials are also looking into reports of at least two other friendly fire encounters that may have killed three US soldiers and wounded 42 wounded.

At about the same time as Simpson's account became known here, a Central Command statement said three US servicemen were killed and five were hurt in a possible friendly fire clash involving an F-15E Strike Eagle aircraft and coalition ground forces.

It provided no further details and a link to the attack in northern Iraq was not apparent.

Also under investigation are reports of an encounter March 27 near the southern city of Nasiriyah in which 37 marines were wounded when two groups fired at each other during an Iraqi attack.

A naval pilot from the US carrier Kitty Hawk was also feared to have been downed by a US Patriot missile over southern Iraq.

Friendly fire has taken an equally heavy toll on British forces, who to date have lost five of their troops in such incidents.

Two British Royal Air Force pilots were killed when their GR4 Tornado was shot down near the Kuwaiti border, again by a US Patriot missile battery. A British soldier also died when according to media reports a US A-10 tankbuster aircraft fired on two armoured vehicles.

In a third incident, two British soldiers were killed when one Challenger 2 mistakenly fired on another.

Military analysts have warned that as war becomes increasingly more complex technologically, with troops possessing weapons of devastating power and lethality, there has been no corresponding decrease in the susceptibility of human beings to make mistakes.

"Because of the complexity of it (modern warfare), it becomes very, very tricky to get the balance right," British army Colonel Ronnie McCourt said here recently.

"No matter what structure you have in place, people get tired and accidents happen."

Friendly fire incidents have increased almost steadily since World War II, when, according to the American War Library's Friendly-Fire Notebook website, 21 percent of fatal and non-fatal casualties were attributed to friendly fire.

The site, which referred to US Defense Department statistics, collects and analyzes data on such incidents.

Friendly fire accounted for 18 percent of fatal and non-fatal casualties in the Korean War, 39 percent in Vietnam and 49 percent in the 1990-1991 Gulf War.

SPACE.WIRE