Tensions are rising in eastern Ukraine after violent clashes left at least two pro-Russia militants dead.
The deadly encounter came as Ukrainian forces are moving in to drive pro-Russia militants out of the east.
Russia is launching new military exercises along the Ukranian border, increasing concerns over the possibility of a military invasion.
Ukraine's acting president said Russia is "openly supporting terrorist killers" in eastern Ukraine. Government buildings in at least 10 cities have been seized by pro-Russia militants.
Meanwhile, Ukraine Foreign Minister Andriy Deshchytisa blasted Russia's most recent military maneuvers, warning his country is prepared to fight any invading troops.
"We will now fight with Russian troops if ... they invade Ukraine. Ukrainian people and the Ukrainian army are ready to do this," Deshchytisa told The Associated Press.