A citizen of Slovakia, a mortar gunner of the militants, has been detained in the town of Ilovaisk in Donetsk region, half of which is now controlled by the Donbas volunteer battalion of territorial defense of Donetsk region and special police battalions, an adviser to the Ukrainian interior minister, Anton Herahchenko, has said.

"A European Union citizen of Serbian descent, who has citizenship of the Slovak Republic and is a resident of the city of Banska Bystrica, was detained near a locomotive depot in the town of Ilovaisk. He had a Slovak passport with a mark confirming that he crossed the Ukrainian border at Zhuliany airport on July 3, 2014," Heraschenko said on his Facebook account early on Tuesday after a conversation with Donbas battalion commander Semen Semenchenko.

"This is the first time the detention of a citizen of a EU country fighting on the side of the terrorists has been confirmed by documents. A court will determine the extent of his guilt," he said.