A security guard watches the UEFA Euro 2016 fan zone site under construction next to the Eiffel Tower | Alain Jocard/AFP via Getty Images Frenchman arrested in Ukraine was planning Euro 2016 attacks: security official French officials address safety concerns in the run-up to soccer tournament.

A French national detained in Ukraine was planning up to 15 attacks in France around the time of this month's European soccer championship, news agencies reported Monday, citing a top Ukrainian security official.

French news outlet M6 reported Friday that a 25-year-old man was arrested by border guards in western Ukraine on May 21 with weapons, including rocket launchers and Kalashnikov rifles, and explosives in his vehicle.

The Interfax news agency quoted Vasyl Hrytsak, the head of Ukraine’s SBU intelligence agency, saying Monday: "The SBU has succeeded in preventing a series of 15 terrorist attacks, which were planned for the Euro 2016 in France, which will open June 10."

The intelligence chief said targets included "a Muslim mosque, a Jewish synagogue, tax collection organizations, police patrol units and numerous other locations," AFP reported.

"He obtained five Kalashnikov rifles, more than 5,000 bullets, two anti-tank grenade launchers, 125 kilograms (275 pounds) of TNT, 100 detonators, 20 balaclavas and other things."

However, French authorities cited by local media reported that they had received no information about an imminent terror threat.

French magistrates opened an investigation, but the anti-terrorism unit is not involved. Investigators suspect the arrested man may have been involved in weapons trafficking and not terrorism, Europe 1 reported, citing an interior ministry source.

High-risk tournament

The soccer tournament has been beset by security concerns following the Brussels and Paris terror attacks.

President François Hollande said Sunday that there was a terrorist threat hanging over the tournament, and that authorities had taken far-reaching measures to ensure fans' safety. He added on France Info: "We should never allow ourselves to be intimidated."

Authorities will deploy more than 90,000 security personnel including 42,000 police officers, 30,000 gendarmes, 5,200 firemen, rescue workers and de-miners, 13,000 private security agents and some 10,000 military personnel.

Many will be charged with protecting "fan zones," closed-off areas where tourists can watch matches on big screens, and which authorities have identified as being particularly vulnerable to attack.

"We are very much focused on stadiums and fan zones, but the need for security is spread across the Paris region," Paris police prefect Michel Cadot said at a press conference Monday, according to Agence France-Presse. "This is a major security challenge."

With police forces under constant strain since last year's attacks, Cadot earlier said that one of the main fan zones, which is at the foot of the Eiffel Tower and can hold as many as 92,000 fans, should be shut down.

Cadot had complained in a leaked note that police would not be able to ensure that rival bands of hooligans would be kept apart. He made no mention Monday of plans to shut down the fan zone in question.

Reports on the alleged plot did not specify whether fan zones or stadiums were targeted. The Ukrainian security chief said the man arrested was angry about his government's immigration policy, the spread of Islam and globalization.