Security fears over the Euro 2016 football championship that kicks off next Friday have been heightened after a Frenchman was arrested in Ukraine with a massive arsenal of weapons he was reportedly planning to use in attacks in France.

The man, named by media as Grégoire M, had three rocket-launchers, about 100 detonators, more than 100 kilos of TNT explosives, and half a dozen Kalashnikov assault rifles in his vehicle when he was detained after trying to cross the border into Poland.

The 25-year-old, who had links to far-Right groups, told police he was planning to use the weapons in possible attacks on synagogues or mosques, according to French media reports.

He was apparently not planning to target any Euro 2016 events, but the weapons seizure will likely heighten tensions over the championships that will take place amid fears of attacks by Isil terrorists.

The man, who is currently being held by Ukrainian authorities pending a possible extradition request from Paris, was arrested on May 21 but reports of his detention only emerged this weekend.