Russia has concentrated more than 150,000 troops on Ukraine's border and in annexed Crimea, the EU's top diplomat Josep Borrell said on Monday after EU foreign ministers were briefed by Ukraine's foreign minister.

"It is more than 150,000 Russian troops massing on the Ukrainian borders and in Crimea. The risk of further escalation is evident," Borrell said, declining to give a source for the figure.

He said no new economic sanctions or expulsions of Russian diplomats were planned for the time being, despite saying that the military build-up on Ukraine's borders was the largest ever.