Katyusha rockets fired on a camp housing Iranian dissidents near Baghdad have killed five members of the opposition group, Iraqi security officials say.
About 40 members of the Mujahedeen-e-Khalq (MEK) group were wounded in Saturday's attack, along with three Iraqi policemen.
MEK calls for the overthrow of Iran's leaders and fought alongside the forces of former Iraqi leader Saddam Hussein in the Iran-Iraq war in the 1980s.
There was no immediate claim of responsibility for the attack on the transit camp, a former American military base known as Camp Liberty.
"At 5:30am around 18 Katyusha rockets landed in the camp, west of Baghdad, killing five people and wounding 42," said an Iraqi policeman at the base, speaking on condition of anonymity.
A government official told Al Jazeera that the government had no way of knowing where the rockets were fired from.
UN urges investigation
The United Nations called on Iraqi authorities to "promptly conduct an investigation" and said its monitors on the ground were following up on the deaths, the first confirmed fatalities as a result of violence at the group's new camp since they moved there last year.
Eliana Nabaa, spokeswoman for the UN mission in the country, said Iraqi officials had told the UN that "all those who were injured were hospitalised immediately".
The MEK, whose leadership is based in Paris, said in a statement that six people were killed and 50 wounded.
A spokesman for the group said they did not know for sure who was behind the attack, but said one likely suspect was
Iran's Quds force - an elite unit of the Revolutionary Guards with a special focus on military operations outside the country.
Camp Liberty is home to about 3,000 residents from the MEK who were moved last year, on Iraq's insistence, from their historic paramilitary camp of the 1980s - Camp Ashraf.
The MEK was founded in the 1960s to oppose the Shah of Iran, and after the 1979 Islamic revolution that overthrew him it took up arms against Iran's theocratic rulers.
It says it has now laid down its arms and is working to overthrow the government in Tehran through peaceful means.
It is no longer welcome in Iraq under the Shia-led government that came to power after US-led forces invaded and toppled Saddam in 2003.
Al Jazeera's Jane Arraf, reporting from Baghdad, said Iraq sees the group as a "terrorist group".
"They [MEK] say they're in danger from the Iranians and the Iraqi government," she said.
"The UN is trying to relocate them, but ultimately they're under the protection of the Iraqi government."
Britain struck the group off its terror list in June 2008, followed by the European Union in 2009 and the US in September 2012.
The US state department holds the group responsible, however, for the deaths of Iranians as well as US soldiers and civilians from the 1970s into 2001.
The MEK has no support in Iran, and no connection to domestic opposition groups.