PARIS/MARSEILLE - Police detained a young man in southern France on Thursday on suspicion that he was planning a revenge attack on the staff of a satirical magazine which published cartoons mocking the Prophet Mohammad.

Anti-terrorism magistrates near the Mediterranean port city of Toulon questioned the 18-year-old after he threatened in a message on Facebook to cut the throats of anyone he could find at the offices of Charlie Hebdo, a judicial source said.

The suspect had no police record but he was already known to security services, the source said, without giving further details.

Police in France are on high alert for attacks by Islamist militants. They were criticized for failing to stop an al-Qaida-inspired gunman shooting dead seven people in March, including three Jewish children, in the southern city of Toulouse.

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