Clashes and explosions were reported in a camp housing Iranian exiles on Sunday, with the group claiming Iraqi troops killed more than 50 of their members, charges officials steadfastly denied.
Officials and the group offered wildly different accounts of the unrest, though, none of which could be independently confirmed.
The US swiftly condemned “the terrible events that took place at Camp Ashraf today.”
“Those found to be responsible must be held fully accountable,” Harf said.
The UN said it was trying to establish what took place and Iraqi Prime Minister Nuri al-Maliki formed a committee to probe the incident.
In addition to the casualties, the People’s Mujahidin Organization of Iran (PMOI), about 100 of whose members were living at Camp Ashraf in Diyala Province near the Iranian border, also claimed security forces set fire to the group’s property in the camp, all of which was denied by Iraqi officials.
Local hospitals reported three Iraqi soldiers were killed and four wounded, which officials attributed to angry camp residents attacking an army brigade responsible for the camp.
However, medics did not report any casualties among Ashraf residents.
The unrest was condemned by the UN’s refugee agency, the UN High Commissioner for Refugees (UNHCR), which did not assign blame for the incidents.
The UNHCR said “it appears that deadly force has been used and that a number of people have been killed or wounded.”
Earlier this year, at least eight people were killed in two mortar attacks on another camp housing the group, also known as the Mujahidin-e-Khalq (MEK).
Officials and MEK spokespeople gave totally different accounts of the latest unrest and it was not immediately clear what caused the explosions and clashes, or the extent of the casualties.
Iraqi police and medical sources said five mortars hit the camp.
A police colonel said that in the aftermath of the rockets, “some angry Ashraf residents came out and attacked the brigade protecting the camp,” killing three soldiers and wounding four in clashes.
A doctor at the main hospital in the provincial capital, Baquba, confirmed the toll.
An Iraqi official responsible for overseeing the camp said the blasts were caused not by mortars, but by oil and gas containers exploding inside Ashraf.
“Not a single soldier entered Camp Ashraf,” Haqi al-Sharifi said. “There was no attack from outside against the camp, but what seems to have happened is that some barrels of oil and gas inside Ashraf exploded. The police are investigating.”
The MEK said that the Iraqi army had entered Ashraf and killed 52 of its members in a “massacre” and set fire to property.
“Scores of PMOI members were wounded and are in critical conditions and a number have also been taken hostage,” MEK spokesman Shahriar Kia said in a statement.
Former Iraqi president Saddam Hussein allowed the rebel MEK to set up the camp during his war with Iran in the 1980s.
About 3,000 MEK members were moved from Ashraf to Camp Liberty, located on a former US military base on the outskirts of Baghdad, last year, but about 100 stayed on at the old camp to deal with leftover property and goods.
Maliki’s committee began its investigation late on Sunday, according to the prime minister’s spokesman, Ali Mussawi, and was expected to report back in the coming days.
The MEK was founded in the 1960s to oppose the shah of Iran, and after the 1979 Islamic revolution that ousted him, it took up arms against Iran’s clerical rulers.