A Frenchman detained last month with a large cache of arms was planning mass attacks during the Euro 2016 football tournament, which starts on Friday, Ukrainian officials say.
The man, identified by French media as Gregoire Moutaux, 25, was arrested on the Ukrainian border with Poland.
Intelligence chief Vasyl Hrytsak said the man had planned 15 attacks and was driven by ultra-nationalist views.
He had amassed guns, detonators and 125kg of TNT, Mr Hrytsak said.
Mr Hrytsak listed bridges, motorways, a mosque and a synagogue among the suspect’s potential targets. He was being prosecuted for arms smuggling and terrorism, he said.
His home in north-east France has been searched by police, who – according to media reports – found a T-shirt bearing far-right insignia. The Ukrainians say he was motivated by hatred of immigration and globalisation.