France's domestic intelligence agency has detained a 26-year-old Russian-Ukrainian man on suspicion of planning a violent act after he injured himself in an explosion, prosecutors said on Wednesday. The news came hours before world leaders gathered in the nation to mark the 80th anniversary of D-Day in Normandy.

The man was treated by a fire brigade on Monday evening "when he suffered serious burns following an explosion," said the National Anti-Terrorism Prosecutor's Office, known as PNAT.

"Products and materials intended to manufacture explosive devices" were found at his hotel room, PNAT said.

According to two sources close to the case, the man stayed at a hotel in the town of Roissy-en-France, home to Paris Charles de Gaulle airport.

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

The man, who has both Russian and Ukrainian passports, was detained on Monday evening, a source said.

On Tuesday, the prosecutor's office opened an investigation into suspected plans to commit a violent act.

A source, asking not to be named, told AFP that the man was from the Donbas region of eastern Ukraine, part of which has been occupied by pro-Russian and Russian forces since 2014. He appeared to have a "pro-Russian attitude" after fighting "for two years for the Russian army", added the source.

France remains on high alert

In an indication of the seriousness of the case, the man is being held by France's domestic intelligence agency General Directorate for Internal Security rather than the regular police.

It is not clear at this stage if the man is suspected of acting alone or in a group.

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

The PNAT has opened an investigation into suspected involvement in a terrorist plot as well as possession of explosives and substances that can be used to make an explosive.

France has raised its security alert to the highest level in the run-up to the Olympic Games in Paris, which run from July 26 to August 11.

This week France is hosting high-profile commemorations of the 80th anniversary of D-Day in Normandy. President Biden, French President Emmanuel Macron, British Prime Minister Rishi Sunak and Canadian Prime Minister Justin Trudeau were together in Normandy to mark the most significant victory of the Western allies in the war.

Mr. Biden is in France through the weekend for D-Day anniversary commemorations and plans to meet with leaders of key allies during his visit. The Secret Service was tracking the Russian-Ukrainian man's arrest but the incident had no impact on the president's movements, CBS News has learned.

The presence of so many foreign leaders in France was one reason why the case has been handed to the anti-terror prosecutors, a source said.

Paris has indicated that President Emmanuel Macron is also seeking to ramp up support for Ukraine, including military backing -- moves that have angered Moscow.

French security services have arrested a Chechen teenager suspected of plotting an "Islamist-inspired" attack on a football game during the Paris Olympic Games, the interior ministry said last month.

At the end of May, before this arrest, the interior ministry said 50 attacks were foiled by French intelligence services since 2017.

Last month, the U.S. State Department issued a worldwide caution security alert, warning of "the potential for terrorist attacks, demonstrations, or violent actions against U.S. citizens and interests."  The threat warning was a result of intelligence citing threats by ISIS against Pride events in parts of Europe, three sources told CBS News. 

In:
• Terrorism
• France