French counterterrorism investigators on Wednesday detained a dual Russian-Ukrainian citizen who seriously injured himself in an explosion two days ago.

He was detained on suspicion of planning a violent act after a homemade explosive device detonated in a hotel in Roissy, on the outskirts of Paris on Monday.

The man was treated by a fire brigade on Monday with prosecutors saying he suffered serious injuries.

What have French authorities said?

According to two sources close to the case, the man was staying at a hotel in the town of Roissy-en-France, where Paris's Charles de Gaulle airport is located.

"Products and materials intended to manufacture explosive devices" were found at his hotel room, the prosecutor's office (PNAT) said. 

"One of these devices had exploded," the prosecutors said. The man suffered head injuries, according to one of the sources.

Specialist anti-terrorism prosecutors in charge of case

The case has been placed in the hands of the specialist anti-terror prosecutors rather than criminal prosecutors. 

Additionally, the man is being held by France's domestic intelligence agency General Directorate for Internal Security (DGSI) rather than the regular police.

Investigators reportedly discovered ammonium nitrate, a cheap explosive favored by terrorists.

French newspaper Le Journal du Dimanche reported that the man is believed to be a Russian spy targeting French military equipment for Ukraine.

France has raised its security alert to the highest level in the run-up to the Summer Olympics in Paris, which run from July 26 to August 11, and the Paralympic Games, which run from August 28 to September 8.

km/jsi (Reuter, dpa, AFP)