A French prosecutor said on Sunday that a man arrested last week after a police raid on a flat near Paris had a direct connection with Islamic State.
Police discovered a stash of explosives in the raid last Wednesday in Villejuif, south of Paris, and found TATP, a product often used by suicide bombers.
A second cache of explosive materials was discovered in a nearby town the following day.
Two men who were arrested were put into formal investigation on Sunday and placed in detention, the Paris prosecutor, Francois Molins, told a news conference. A third suspect was released with no charges.
"Analysis from the material seized showed one of the suspects had been in direct contact in August 2016 with Rachid Kassim via Facebook," Molins said.
Kassim, believed to be a senior Islamic State militant, was targeted by the US military in a strike near the city of Mosul, Iraq, earlier this year.
TATP has been used by militants in several attacks in Western Europe in recent years, including Manchester in May, Brussels in 2016 and Paris in 2015.
More than 230 people have been killed by Islamist-inspired attackers in the past three years in France, which along with the United States and other countries are bombing Islamic State bases in Iraq and Syria.