Ukrainian Security Service (SBU) officers carried out an operation to prevent a series of terrorist attacks on the territory of France, which were planned for the time of the Euro 2016 European football championship, SBU Chief Vasyl Hrytsak has said.

"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," Hrytsak said at a briefing in Kyiv on Monday.

He said the Security Services did a great job.

"In December 2015, we found out that a French citizen arrived in Ukraine posing as a volunteer. He began establishing contacts with representatives of military units in the east of our country," Hrytsak said.

The SBU chief said the Frenchman promised volunteer assistance, bringing equipment and other things to Ukraine. However, he then began to take an interest in the possibility of buying weapons, explosives, and other means of destruction in Ukraine, Hrytsak said.

According to investigators, the Frenchman acquired five Kalashnikov rifles, more than 5,000 cartridges, two hand-held anti-tank grenade launchers and 18 shells for them, 125 kilograms of TNT, 100 detonators, and 20 balaclavas.

"I think there is no need to explain what destruction could be caused by 125 kilograms of explosives," Hrytsak said.

The SBU chief said agents worked on this case for six months, and investigators documented every step of the detainee.

Hrytsak said the French citizen was detained in Yahodyn checkpoint on the border with Poland on May 21.

French media reported earlier that a French citizen, who could have been planning attacks in the run-up to Euro 2016, was detained on the Ukrainian-Polish border with an arsenal of weapons and explosives. According to media reports, the man was detained on 21 May.

On June 4, the State Border Service of Ukraine reported that a French citizen was detained at the checkpoint of Yahodyn on the border with Poland. They didn't disclose any other details.