Russian officials said Wednesday that Moscow will create three new divisions of about 10,000 soldiers each to counter NATO’s planned troop buildup in Eastern Europe.

“The Defense Ministry is taking a series of measures to counter the expansion of NATO forces in direct proximity to the Russian border,” Russian Defense Minister Sergei Shoigu said.

Shoigu said the new Russian divisions would be formed by the end of the year. Reuters, citing Russian media, reported that the Russian divisions would include about 10,000 soldiers each.

Western officials told The Wall Street Journal last week that NATO is planning to send about 4,000 troops to Poland and the Baltic states of Estonia, Latvia and Lithuania.

NATO Secretary General Jens Stoltenberg said the alliance’s planned buildup in the Baltics wouldn’t have happened if Russia didn’t insert itself into the Ukraine conflict in 2014. Stoltenberg said NATO’s deployment was a reaction to Russian aggression.

The announcement of heightened military measures on both sides comes after a serious of incidents in the skies and the Baltic Sea involving U.S. jets, a U.S. destroyer and Russian warplanes.

Last week, a Russian Su-27 performed a barrel roll over a U.S. spy plane in the Baltic Sea. Russia said the U.S. plane was coming too close to a military base and had its transponder turned off.

Su-27s and a military helicopter also simulated attack passes near the USS Donald Cook, flying up to 75 feet within the Navy destroyer last month in the Baltic Sea.

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