Moscow on Tuesday said active U.S. military support to Kyiv was a serious challenge for Russia's security and accused Washington and NATO of turning Ukraine into a "powder keg" with increasing arms supplies, Russian agencies reported, citing the foreign ministry.
Russia would do everything possible to ensure its security in the event of an escalation in Ukraine, agencies quoted Deputy Foreign Minister Sergei Ryabkov as saying.
Earlier on Tuesday, Ryabkov warned the United States to ensure its warships stayed well away from Crimea "for their own good", calling their deployment in the Black Sea a provocation designed to test Russian nerves.
ATO Secretary-General Jens Stoltenberg called on Russia on Tuesday to withdraw troops that the alliance says Moscow is massing on Ukraine's borders.
"In recent weeks Russia has moved thousands of combat-ready troops to Ukraine's borders, the largest massing of Russian troops since the illegal annexation of Crimea in 2014," Stoltenberg said.
"Russia must end this military build-up in and around Ukraine, stop its provocations and deescalate immediately," he said at a news conference with Ukraine's Foreign Minister Dmytro Kuleba. Kuleba said Kyiv wanted a diplomatic solution.