French prosecutor said on Friday that one of the suspects in a foiled attack on a French military base was instructed by an Islamic State militant in Syria to "hit" France.

French prosecutor said on Friday that one of the suspects in a foiled attack on a French military base was instructed by an Islamic State militant in Syria to "hit" France.

The youngest of three suspects in custody -- aged only 17 and identified as Ismael K. -- was given the order when it became clear he would not be able to leave the country to wage “jihad” in Syria because he was under surveillance, Paris prosecutor Francois Molins said.

Four young men, including a formal naval signalman, were arrested in dawn raids on Monday, suspected of "planning to commit a terrorist act" at a French military base in the south of the country.

The youngest, 16, was quickly released, but the other three were plotting to kidnap and behead a member of the military on film around the end of December or beginning of January 2016, according to Molins.

They came into contact with each other via social networks and formed a plan to go to Syria to wage “jihad” alongside other ISIL (so-called Islamic State in Iraq and Levant) extremists.

However, Ismael K.'s mother became concerned about his radicalization and contacted the authorities. He was subsequently interviewed by counter-terrorism officials and was aware he was under surveillance.

For this reason, the trio used encrypted messaging systems and applications, the prosecutor said.

"There was in particular an exchange between Ismael K. and an individual currently fighting with IS in Syria who -- given it was impossible for him to leave France -- told him to 'hit on the ground in France'," the prosecutor said.