The Ukrainian military said on Thursday it had carried out tank drills in the eastern Donetsk region, part of an increase of military activity by both Ukraine and Russia that has raised the risk of open war between the two ex-Soviet neighbors.
Ukraine's foreign minister earlier on Thursday had warned Russia that an attack on his country would incur "political, economic and human losses" and would be too costly.
Russia has been building up forces near its border with Ukraine, and Kyiv, the United States and NATO have voiced concerns about a possible Russian attack - a suggestion the Kremlin has dismissed as false. Ukrainian troops have fought Russian-backed separatists in a conflict in eastern Ukraine that Kyiv says has killed 14,000 people since 2014.