More than 300 Ukrainian troops have crossed into Russia during heavy fighting with pro-Russian separatists.
A Ukrainian security spokesman, Andriy Lysenko, said the 311 soldiers and border guards “had to cross into Russian territory” at the Gukovo checkpoint in eastern Ukraine.
Ukraine is trying to get them back now through diplomatic channels, he said.
Earlier a Russian security official said 438 Ukrainian troops had been given refuge in Russia as “defectors”.