A deadly attack on a camp near Baghdad housing Iranian exiles Saturday killed two residents, the second such assault on the group this year as its members await resettlement outside Iraq.
It was not immediately clear who was behind the attack involving at least half a dozen mortar rounds, which came as Iran tallied ballot papers from Friday's presidential election there.
"I can confirm that there was a deadly attack," Eliana Nabaa, spokeswoman for the United Nations mission in Iraq, told AFP.
A police colonel, speaking on condition of anonymity, put the toll at three dead and 11 wounded from six mortar blasts.
But Shahriar Kia, a spokesman for members of the People's Mujahedeen Organisation of Iran, or the Mujahedeen-e-Khalq (MEK), at Camp Liberty, said two people were killed -- one woman and one man -- and more than 30 wounded.
"Dozens" of rockets hit the camp, setting fire to multiple trailers, he said.
Kia criticised the United Nations for not agreeing to move Liberty residents back to their original base at Camp Ashraf near the border with Iran.
The MEK's parent organisation, the National Council of Resistance of Iran, issued a statement in Paris sharply criticising the UN for inaction and making "false promises".
Saturday's attack was the second assault this year on Camp Liberty, which has some 3,000 residents.
In February, dozens of mortar rounds and rockets fired at the camp killed six people, according to the US State Department.
UN special envoy to Iraq Martin Kobler condemned the attack, and said the "tragic violence has occurred despite their (the UN's) repeated requests to the government of Iraq to provide Camp Liberty and its residents with protective measures, including T-Walls," referring to concrete walls that protect against explosions.
"Today's second terror attack on Camp Liberty is a reminder to third countries to come forward with serious offers to resettle Camp Liberty residents outside Iraq," Kobler added in a statement.
The head of the UN's refugee agency Antonio Guterres, meanwhile, described the attack as an "unacceptable and horrific act of violence".
MEK members were moved to Camp Liberty late last year at Iraq's insistence from Ashraf, their historic paramilitary camp of the 1980s.
Camp Ashraf was the base that now-executed dictator Saddam Hussein allowed the group to establish in Diyala province during Iraq's eight-year war with Iran.
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.
It says it has now laid down its arms and is working to overthrow the Islamic regime in Iran by peaceful means.
Britain struck the group off its terror list in June 2008, followed by the European Union in 2009 and the United States in September last year.
But the US State Department holds the group responsible for the deaths of Iranians as well as US soldiers and civilians from the 1970s to 2001, and in its note about delisting the MEK it stressed it had not forgotten the group's militant past.
A senior US official said at the time that Washington does "not see the MEK as a viable opposition" within Iran.
Several countries have made offers to take in members of the group. Most recently, 14 MEK members left Liberty last month for Albania, which has offered to take in more than 200.
The latest attack came as ballots were being counted from neighbouring Iran's presidential election, which was won by moderate cleric Hassan Rowhani.