WASHINGTON (Reuters) - The United States finds reports of Russian military movements on Ukraine’s border “credible,” has asked Moscow to explain the “provocations” and is ready to engage on the situation, the U.S. State Department said on Monday. The reported Russian troop buildup and movements bordering eastern Ukraine have become the latest point of tension in icy U.S.-Russian relations less than three months after U.S. President Joe Biden took office. State Department spokesman Ned Price told a news briefing that the United States would be concerned by any effort by Moscow to intimidate Ukraine whether it occurred on Russian territory or within Ukraine. He declined to say whether the United States believed Russia was preparing to invade the neighboring former Soviet republic. Later on Monday, a State Department spokesperson told Reuters that the United States is “open to engagement with Moscow” on the situation, describing as “credible” reports of Russian troop movements on Ukraine’s border and Crimea, the peninsula seized by Russia in 2014. The movements, the spokesperson said, were preceded by violations of a July 2020 ceasefire that killed four Ukrainian soldiers and wounded four others. “We call on Russia to refrain from escalatory actions,” the spokesperson said. The comments followed a telephone call on Friday in which Biden reassured his Ukrainian counterpart, Volodymyr Zelinskiy, of “unwavering support” in Ukraine’s confrontation with Russia-backed separatists holding parts of the country’s eastern Donbas region. Russia on Monday denied that Russian military movements posed a threat to Ukraine and dismissed fears of a buildup even as it warned that it would respond to new Ukrainian sanctions against Russian companies. White House press secretary Jen Psaki told reporters that “recent escalations of Russian aggression and escalation in eastern Ukraine” is “something we’re watching closely.” Biden’s call with Zelinskiy came after the NATO alliance expressed concern over what is said was a large Russian military buildup on Russia’s side of the border with eastern Ukraine. “We’ve asked Russia for an explanation of these provocations,” Price said. “But more importantly, what we have signaled with our Ukrainian partners is a message of reassurance.” Pressed on whether the United States viewed troop movements on Russia’s side of the border as intimidation of Ukraine, Price responded, “Of course, the Russians have for quite some time sought to intimidate and bully their neighbors.” Ukraine, Western countries and NATO accuse Russia of sending troops and heavy weapons to prop up proxies who seized a swath of the eastern Donbas region in 2014. Moscow says it provides only humanitarian and political support to the separatists.