Human rights activists accused Iraqi forces Wednesday of carrying out a bloody attack on a camp of Iranian exiles in which 52 people were shot dead.

A German rights groups working with a Washington-based lawyer claimed their 70-page report "confirms the direct involvement of the government of Iraq in the attack" on September 1.

Calling for a UN investigation into the attack, the Aachen-based Rights for Migrants group said interviews with the 42 survivors of the attack on Camp Ashraf, in central Diyala province, "unequivocally puts Iraqi forces at the scene."

It alleged Iraqi police moved blockades guarding the camp to allow access to about 120 armed attackers, who were dressed in uniforms identical to those worn by a special Iraqi forces division and spoke with Iraqi accents.

"For two hours, the attackers scoured the camp, killing 52 and destroying millions of dollars in property. Every individual killed was shot in the head or neck, and many were handcuffed before being executed," the report said.

It maintained that due to the close proximity of about 1,200 Iraqi military and police forces stationed nearby it was "impossible that any rogue group of attackers could have entered Camp Ashraf without the knowledge, blessing or direct authorization of the Iraqi government."

It also says seven people were taken hostage, and were now reportedly being held in detention centers near Baghdad.

The Iraqi government has denied any involvement in the attack on the camp where a few members of the People's Mujahedeen Organization of Iran were residing.

The rest of about 3,000 members of the group have already been relocated to a former military base, known as Camp Hurriya, or Liberty, on the outskirts of the Iraqi capital.

A US official said that while the attack on the camp "was reprehensible," there was "no credible information to date that the Iraqi government was in any way involved."

He called for "an international humanitarian effort" to resettle the remaining 2,900 people in Camp Hurriya in a third country.

"So long as they are in Iraq there is nothing that can be done to totally protect them it is simply not possible," the official added.

"We need a place for them to go."

He said the attack had been raised in morning talks between US Vice President Joe Biden and visiting Iraqi Prime Minister Nuri al-Maliki.

The People's Mujahedeen initially took up arms against Iran's shah and then set its sights on toppling the clerical regime that came to power after the 1979 Islamic Revolution.

They were allowed by late Iraqi dictator Saddam Hussein to operate in the country, settling in Camp Ashraf. But Iraqi officials are eager now for them to be resettled.

The group says it has renounced violence and has enlisted high-profile US supporters to their cause.

Last year, the State Department removed the group's designation as a terrorist organization following similar decisions in Europe.

Albania and Germany have agreed to take in about 310 exiles between them, but the UN has struggled to resettle most of them.