Russia says will retaliate if U.S. weapons stationed on its borders

"If heavy U.S. military equipment, including tanks, artillery batteries and other equipment really does turn up in countries in eastern Europe and the Baltics, that will be the most aggressive step by the Pentagon and NATO since the Cold War," Russian defense ministry official General Yuri Yakubov said.
"Russia will have no option but to build up its forces and resources on the Western strategic front," Interfax news agency quoted him as saying.

http://www.reuters.com/article/2015/06/15/us-russia-usa-europe-idUSKBN0OV17A20150615