Russia is holding military training exercises in Transdniestria, a breakaway part of Moldova that is now a focus of tension following Russia's annexation of the Ukrainian region of Crimea.
NATO's top military commander said on Sunday he was worried Russia might have its eye on Transdniestria, a largely Russian-speaking region that borders western Ukraine.
Transdniestria, which has a population of half a million, has run its own affairs since 1992 after a brief war against the Moldovan government.
Russia has a permanent garrison of peacekeepers there.
Russia held several military drills during the political upheaval in Ukraine. Some were conducted close to Ukraine's eastern border.