A commercial helicopter carrying security contractors has been shot down by missile fire north of the Iraqi capital, killing all 11 people aboard, including six Americans, officials said.

Bulgaria's Defense Ministry said on Thursday that the helicopter was downed by missile fire and that the three crew members were Bulgarian.

A Canada-based charter company said the two additional passengers were bodyguards from Fiji, but the Bulgarian Transport Ministry said they were from the Philippines.

The Philippine mission in Baghdad said it had no information that any of its nationals were on the helicopter.

Security contractor

The six Americans worked for security contractor Blackwater USA, the US Embassy said. The North Carolina-based contracting company provides security for US State Department officials in Iraq.

Two American military officials in Baghdad initially said the helicopter was contracted by the US Defense Department, but the US Embassy later said that was untrue. It gave no information on the contractor.

It was unclear whether the civilians' employers were under contract to the Pentagon or the US State Department, US

officials in Washington said.

The helicopter was owned by Bulgaria-based Heli Air and chartered by Toronto-based SkyLink Aviation Inc., said SkyLink air operations manager Paul Greenaway. The helicopter was flying to Tikrit, he said.

Greenaway said the six Americans were "doing some sort of security work."

Responsibility

A group campaigning against the US in Iraq claimed responsibility for the attack on the helicopter, according to an internet statement.

"The Islamic Army in Iraq claims responsibility for bringing down a ... cargo aircraft and killing all those on board," said the short posting on a website, adding that a fuller statement and a video film of the attack would follow.

In Ramadi, 115km west of Baghdad, a roadside bomb wounded one soldier in a US convoy. When another US soldier fired his machine gun at a suspected Iraqi ambush site, a female Iraqi civilian was wounded, then died in a hospital, US officials said.

Hours later, gunfire erupted downtown, and an Associated Press photographer at the scene saw a young boy lying dead in a street near three smoldering cars. Sporadic gunfire continued for about two hours, the photographer, Bilal Hussein, said.

When it subsided, Iraqis pulled the charred body of an adult from one of the burned cars, Hussein said.

It was not clear how the two had been killed.

The US military had no immediate information on the second incident.

Bodies identified

Meanwhile, the Iraqi Defense Ministry identified 19 bullet-riddled bodies found Wednesday in Haditha, 220km northwest of Baghdad, as fishermen, not soldiers as initially rumored.

Investigations indicated the men had come from the southern Diwaniya and Najaf provinces to fish in Tharthar lake when they were captured by insurgents, taken to the soccer stadium at nearby Haditha and shot, said Saleh Sarhan, the ministry's chief spokesman.

He did not say how the victims had been identified or why they might have been captured.

Also on Thursday, a bomb targeting Western workers in Iraq exploded, killing two security contractors.

The blast hit a car carrying foreign contractors on Thursday morning on the highway to Baghdad's airport, one of the most dangerous stretches of road in Iraq, a police spokesman said.

Aljazeera reported the two killed were US contractors. 

Three 4WD vehicles carrying civilians were heavily damaged in the explosion, police said.

Convoy attacked

Aljazeera reported that the explosion was caused by a car bomb targeting a US convoy near al-Amil neighbourhood.

Iraqi journalist Muhammad Abd Allah told Aljazeera an Iraqi driver was also wounded in the attack and was transferred to a nearby hospital.

No other casualties were immediately reported, but one of the vehicles was consumed by flames, and white smoke rose from another one, police Captain Hamid Ali said.

All three vehicles appeared to have been blown off the road by the impact of the explosion, witnesses said.

The road to the airport is only a few kilometres long and flanked by US military bases.

Abd Allah said al-Matar (airport) Road was known as ''Death Road''

PHOTO CAPTION

A video grab shows the wreckage of a Russian-built commercial helicopter in Baghdad, April 21, 2005. (Reuters)