Man is said to have been arrested in late May on the border with Poland, carrying 125kg of TNT
Several planned terror attacks on the Euro 2016 tournament in France have been thwarted, according to a Ukrainian security chief.
The head of the state's security services said a Frenchman was detained in the country after making contact with illegal armed groups to buy guns and explosives.
It is claimed that he intended to target Muslim and Jewish places of worship, administrative buildings and infrastructure such as bridges and railways.
Vasily Gritsak said the unnamed man was arrested in late May on the border with Poland, carrying 125kg of TNT.
The suspect had been tailed since December, Mr Gritsak said, and was seen buying five machine guns, two rocket-propelled grenades, and other weapons.
At a news conference he said: "The Frenchman spoke negatively about his government's actions, mass immigration, the spread of Islam and globalisation, and also talked about plans to carry out several terrorist attacks."
Last week, the US State Department issued a "potential terrorist attacks" warning for Americans planning to travel to Europe.
The travel alert, which expires on August 31st, made no mention of specific threats to Euro 2016 matches or other events, but warned US citizens to "exercise vigilance" and "avoid crowded places".
France's national stadium, the Stade de France, was one site targeted during the 13 November Paris attacks that left 130 people dead.
Suicide bombers detonated explosive belts near gates at the stadium as France played Germany in a friendly match.
In recent months, French special forces have been preparing to deal with simulated attacks during the tournament by carrying out several practice runs with emergency teams.