Russian President Vladimir Putin on Sunday ordered the country’s Defense Ministry to put deterrence forces on high alert.
Putin held a meeting with Russian Defense Minister Sergei Shoigu and Chief of General Staff Valery Gerasimov in Moscow. He said leaders of major NATO countries have made "aggressive statements" about Russia.
Russia's deterrence forces also include nuclear weapons and hypersonic missiles.
Putin ordered the military intervention on Thursday, days after recognizing two separatist-held enclaves in eastern Ukraine.
At least 368,000 Ukrainians have fled to Poland, Hungary, Romania, Moldova and other countries since then, according to the UN Refugee Agency.
Western powers have imposed financial sanctions on Moscow, and decided to supply Ukraine with weapons and ammunition.