Russia threatened Monday to boost forces on the borders of NATO states and position tactical Iskander missiles in the Russian enclave in Kaliningrad on the Baltic Sea if the U.S. goes ahead with a modest buildup of tanks, artillery and other heavy equipment in Eastern Europe.

"Russia will have no other choice but to boost its military potential along its western borders" to counter the U.S. move that is still in the planning stages, Russian Gen. Yury Yakubov, a senior Defense Ministry official, told the Russian Interfax news agency.

Over the weekend, the New York Times reported that the Defense Department was planning to pre-position M1A1 Abrams tanks and other equipment for about 5,000 troops in states that could include Poland, Romania, Bulgaria and the Baltic states of Estonia, Latvia and Lithuania.

At the Pentagon on Monday, spokesman Col. Steve Warren said the pre-positioning plan was evolving and should not be considered a threat to Moscow.

He said equipment for a battalion-sized element had been sent to Europe two years ago and in March approval was given to send equipment for a second battalion.

Planning is underway to equip a brigade-sized element but nothing has been decided, Warren said, adding that, "This is purely positioning equipment to better facilitate our ability to conduct training."

Yakubov dismissed the Pentagon's claims. "If America's heavy arms, be it tanks, artillery systems or other heavy military hardware, are deployed to Eastern Europe and the Baltic States, it will be the Pentagon's and NATO's most aggressive step since the end of the Cold War a quarter of a century ago," he said.

Yakubov said a particular focus of Russia's counter-measures would be on Kaliningrad, the former German port of Konigsberg, situated between Poland and Lithuania on the Baltic Sea and now the headquarters for Russia's Baltic fleet.

"Firstly, the forces stationed along the perimeter of Russia's western border will be strengthened to include forming new tank and artillery capabilities," Yakubov said. "The missile brigade in the Kaliningrad region is also going to be rearmed faster to begin using the new tactical missile systems -- Iskander," he said.

For months, Poland and the Baltic states have been pressing the U.S. to boost the number of rotating training forces in their countries and also to consider establishing permanent bases.

Over the weekend, Polish Defense Minister Tomasz Siemoniak and Lithuanian Defense Minister Yukos Olekas both confirmed that discussions were underway with U.S. Defense Secretary Ashton Carter on plans to boost forces in Eastern Europe.

-- Richard Sisk can be reached at Richard.Sisk@military.com.