The attack was planned for the city of Orleans
French police have prevented an attack on police and army personnel in the central city of Orleans, an official has said.
Two Frenchmen, aged 20 and 24, were being held for questioning, Interior Minister Bernard Cazeneuve said.
Both men are believed to have been in contact with another Frenchman, currently thought to be in Syria.
The Syrian connection is suspected of organising the plot, sources said.
In particular, the suspects aimed to attack a military barracks as well as police stations, a police source told Reuters.
They sought to seize weapons and to recruit other attackers, the source said
Mr Cazeneuve said 10 attacks had been prevented this year in France.
The minister also revealed that 3,414 people had been turned away from France's borders since last month's Paris attacks.
They were refused entry "due to the risk they present to security and public order," said Mr Cazeneuve.
The country suffered its worst atrocity for decades last month when Islamist militants killed 130 people in Paris.