MOSCOW - A senior Russian Defense Ministry official warned on Monday that Moscow would boost its forces on its Western flank should the United States store heavy arms in the Baltic states and eastern Europe.A US official said over the weekend that Washington planned to store heavy military equipment in the Baltics and eastern Europe to reassure allies unnerved by Russia's role in Ukraine and to deter aggression.The Russian official, General Yuri Yakubov, was quoted as saying any such move would be "the most aggressive step by the Pentagon and NATO" since the Cold War."Russia would be left with no other option but to boost its troops and forces on the western flank," Yakubov was quoted as saying by the Interfax news agency.He said Russia would first add new tank, artillery and air units on its western border. It would also accelerate the deployment of new Iskander missiles in the Kaliningrad enclave and shore up its troops in Belarus, he said.Poland and Lithuania have confirmed they are in talks with Washington on stationing heavy arms in warehouses in the region.Kremlin spokesman Dmitry Peskov declined to comment. "There were no statements from the United States to that end so I have no comment for now," he told a conference call with journalists. "We will comment if there is a statement."He said Russian officials were not in touch with their US counterparts at the weekend to learn more about the plans that come as ties between Moscow and the West have hit new lows over the conflict in Ukraine.Russia has long protested against what it describes as Western attempts to encroach on its territory, including by bringing former Soviet republics and countries once in its orbit in Soviet times into the NATO military alliance.