France has arrested the webmaster of a jihadist site on charges of "provoking" terrorism, prosecutors said Thursday, just as the government warned that hundreds of homegrown Islamist militants were signing up to fight in Syria.

The 26-year-old, identified as "Romain", was detained Tuesday for his role as administrator of the Ansar al Haqq website, a "reference" for the radical Islamist movement, and as a translator of magazines put out by militant group Al Qaeda in the Arabian Peninsula (AQAP), Paris prosecutors said.