French President Francois Hollande has vowed the threat of extremism will not stop Friday’s European Championship football tournament from being successful – even as intelligence chiefs revealed details of a deadly terror plot.

Mr Hollande told France Inter radio that precautionary measures, including the deployment of a 90,000-strong security force, will ensure safety at the matches taking place in 10 French cities.

The premier said France decided to go ahead with Euro 2016 despite two waves of attacks last year, and to make it a “festival for people and for sports”.

But he said spectators at the month-long tournament must accept security checks as they enter stadiums and fan zones.

Mr Hollande added that “this threat, alas, will exist for a long time so we must guarantee this great event ... is successful. It will be.”

His comments were overshadowed, though, by a statement from the Ukranian secret intelligence service the SBU.

It revealed how it had thwarted a plot to attack the tournament in France by arresting a heavily-armed Frenchman.

The man – named by French regional newspaper L’Est Republicain as Gregoire Moutaux – was held after investigators raided his home in Nant-le-Petit near the eastern city of Nancy in late May.

The SBU, said it had followed the man since December and allowed him to purchase five machine guns, two rocket-propelled grenade launchers, 125kg of TNT, 100 detonators and other weapons.

He also bought 20 balaclavas before he was arrested at the Yahodyn border crossing between Ukraine and Poland last month, authorities said.

French television network M6 reported that investigators found T-shirts of an extreme right group.

Ukrainian authorities released photos of a fair-haired man, with his face blurred, holding various weapons, as well as a video of the arrest which showed Swat officers dragging the man out of a white minivan and putting him on the ground of what looked like a car park with his face down.

However, the Paris prosecutor’s office, which handles terrorism cases at a national level, said no investigation had been opened yet.

The SBU said the Frenchman became known to the agency last year during his stay in eastern Ukraine, and where he was “trying to establish ties with Ukrainian troops under the guise of volunteering”.

Vasyl Hrytsak, the security agency’s chief. said the SBU “has managed to foil a series of 15 terrorist attacks which were planned to target France before and during” Euro 2016.

The SBU did not identify the man but said the suspect wanted to protest against his government’s migration policies and the spread of Islam.

It said he planned attacks on bridges, railways and other infrastructure for Euro 2016.

A spokesman for the SBU said. “He said that he wanted to perpetrate acts of terror in protest.”

Paris police prefect Michel Cadot declined to comment on the information from Ukraine, saying only that “there is no specific threat against any (Euro 2016) site”.

Ukraine’s intelligence agency had initially planned to keep a lid on the investigation, but decided to go public after information began to leak to media organisations.