PARIS, April 28 (AFP) - Five suspected Islamic militants have been detained in France by intelligence agents who believe they were part of an operation to send volunteers to fight against the US army in Iraq, officials said Thursday.  

The four suspects arrested Sunday in the Paris area and a fifth detained Monday in the southern port of Marseille were placed in preventive detention, sources close to the investigation said.  

One of the five suspects, 39-year-old Moroccan national Said Al-Maghrebi, had been sought for months by several police forces across Europe.  

They were arrested as part of an anti-terrorist investigation launched last September after evidence emerged of a so-called "Iraqi network" recruiting Islamic militants to fight US forces there.  

In January, 11 suspected Islamic militants were taken into custody including 23-year-old Farid Benyettou, who along with two others has been placed under investigation for "criminal association related to a terrorist enterprise".  

French police believe Benyettou was the mastermind behind the recruitment operation, which allegedly sent young men to wage jihad, or holy war, against US-led forces in Iraq.  

An anti-terrorism expert said the operation was "less of an organized cell than a scattered mosaic of spontaneous groups" working to send fighters to Iraq.  

Al-Maghrebi "is not some young birdbrain. He's left his mark on other operations, has shown other jihadist tendencies," a source close to the probe said.  

The Moroccan allegedly spent time in Afghan terror training camps run by Osama bin Laden's Al-Qaeda network. Upon his return, he tried in vain to go to Chechnya, where separatist rebels are battling Russian forces.  

"He has an active past," the source said.  

Al-Maghrebi was preparing to leave for Iraq, via the Syrian capital Damascus, when he was apprehended on Sunday in the Paris suburbs.  

Intelligence agents believe there are between 15 and 30 French nationals with the insurgents in Iraq, and that at least four have been killed in clashes with the US army.  

Investigators said in January that some of the 11 suspects detained at that time had considered violent attacks on French targets, but never got to the planning stage.