Russia's envoy to NATO has warned that Moscow will respond to a buildup of the alliance's forces near Russian borders.

Alexander Grushko said in televised remarks Monday that the deployment of NATO forces in eastern Europe "can't be left without a military-technical answer." He insisted that "Russia won't compromise its security interests," but wouldn't say what specific steps the Kremlin could take.

With Russia's ties with the West ravaged by the Ukrainian crisis, the U.S. and its NATO allies have deployed additional weapons and held exercises in central and eastern Europe. The Pentagon plans to quadruple what it spends on its troops and training in Europe as part of efforts to deter Russia.

Moscow has long criticized the NATO activities on its doorstep as a threat to its security.