Five suspects arrested in and around Paris were French Islamists planning a terror attack, French Interior Minister Brice Hortefeux has said.
The five were detained on suspicion of having trained as militants in the Afghan-Pakistan border region, security sources said at the time.
But Mr Hortefeux said only one of the five had visited Afghanistan while others had planned to go to Pakistan.
One of the four men and one woman had been ready to die, he added.
Al-Qaeda leader Osama Bin Laden warned France last month that its planned ban on the Islamic full-face veil in public places and its involvement in the war in Afghanistan justified attacks on its nationals.
Mr Hortefeux said then that the country faced a real terror threat and he urged "total vigilance".
The five suspects are all French nationals, some of them of Algerian origin, and "clearly belong to the radical Islamist movement", the minister told reporters.
"What we can say is that, over the last few days with these arrests... there was what we call a conspiracy to prepare a terror attack," he said on a visit to police and soldiers at Montparnasse railway station in Paris.
The suspect who visited Afghanistan "was unquestionably very familiar with jihadi internet sites", according to the minister.
Mr Hortefeux went on to say that one of the suspects had been involved in an alleged plan to murder the head of the grand mosque in Paris, Dalil Boubakeur.
The alleged plot to kill Mr Boubakeur was "taken all the more seriously" because a wave of terror attacks on France in 1995 began with the killing of an imam, the minister said.
Mr Boubakeur has been under police protection since death threats against him were reported in September.
Eight people were killed and more than 100 wounded in the attacks, which were organised by Algerian Islamist militants.
Alain Chouet, former chief of France's DGSE foreign intelligence service, said France faced a "real and permanent threat".
"When we have five million Muslims in the country... if we have one in 10,000 that decides to turn to violence, that makes for a healthy reservoir," he was quoted as saying by Reuters news agency.