French police on Thursday detained Iraqi official Sadeq Kazem for questioning after a member of the Iranian opposition filed a complaint alleging torture and war crimes, a judicial source said.
Kazem runs Camp Liberty, where People's Mujahedeen of Iran militants are being moved from their long-time base of Camp Ashraf, the scene of deadly raids by Iraqi forces in 2009 and 2011.
The Iranian said he was detained and tortured at Camp Ashraf on Kazem's orders in 2009.
Iraqi forces carried out raids on the camp in July 2009 and April 2011 that were said to have left 11 and 36 people dead respectively.
The unnamed Iranian said Iraqi forces captured him along with 35 other Camp Ashraf residents on 28-29 July 2009 and held him for 72 days during which he was tortured on Kazem's orders, according to court papers seen by AFP.
The Iranian said he was detained, hit on the head and taken to a police cell where he was held with around 30 other prisoners.
Kazem was detained as he was in France as part of a trip to Europe by an Iraqi government delegation after the Iranian filed the complaint on Wednesday.
Late Iraqi dictator Saddam Hussein had allowed the Mujahedeen to set up Camp Ashraf after he launched the 1980-88 war with Iran in which the group reportedly fought alongside his forces, and provided financial backing.
The aim of the process is eventually to see the exiles resettled outside Iraq.
The left-wing People's Mujahedeen, which has been on the US terror blacklist since 1997, says it has now renounced violence. It was founded in the 1960s to oppose the shah of Iran, but took up arms against the country's new clerical rulers after the 1979 Islamic revolution.
Under a deal between the UN and Iraq, 3,000 members of the People's Mujahedeen, also known as the Mujahedeen-e Khalq (MEK), are to relocate from Camp Ashraf to Camp Liberty.
But although about two-thirds of the refugees had decamped, the process has now stalled and no new relocations had happened since May 5.
The MEK has called on the United States to remove it from its list of terrorist organisations, and a US district appeals court has ruled that US Secretary of State Hillary Clinton must make a decision by October 1.