Sarkozy, several of his ministers and other politicians received envelopes within the past two weeks containing a 9mm cartridge and identical letters from an unknown sender with threats like "you are all dead men walking".

The man had been reported by his former wife, who told investigators in the southern city of Montpellier he had sent her similar messages in the past, a police source said.

The man, a computer specialist, denied sending the letters to Sarkozy and the other politicians. Investigators found no evidence linking him to the threats and he was released without charge late on Thursday.