PARIS (Reuters) - French judges have placed two people under formal investigation and detained them on suspicion of wanting to travel to Syria or planning attacks in France, a judicial source said on Saturday.

They were arrested last Tuesday along with a third person by French intelligence agents in the towns of Clermont-Ferrand and Marseille, and in the Paris region.

The two are facing charges of criminal conspiracy to commit a terrorist act, and possession of weapons, the judicial source said. The third person was released.

The source said there was a possible link between the two and those arrested in a separate raid on Feb. 10 in the town of Montpellier on suspicion of planning an imminent attack in France.

France is under heightened alert since January 2015 following a spate of attacks by Islamist militants that has killed about 230 people.