WASHINGTON, April 5 - The United States has asked Russia to explain recent “provocations” on Ukraine’s border, the US State Department said on Monday, after reported Russian troop enlargement and movements drew international concern last week, Reuters reported.

The department said reports on Russian movements bordering eastern Ukraine, which have become the latest point of tension in icy US-Russian relations less than three months after US President Joe Biden took office, were “credible”.

Speaking during a press briefing on Monday, State Department spokesman Ned Price said the US would be concerned by any effort by Moscow to intimidate Ukraine whether it occurred on Russian territory or within Ukraine.

The department said it is ready to engage on the situation.

“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.”

Russia said on Monday it was in high-level contact with the United States about tensions over Ukraine and dismissed fears of a Russian military buildup even as it vowed to respond to new Ukrainian sanctions.

"We are in contact with the Americans, this is happening at a high level," Russia's Deputy Foreign Minister Sergei Ryabkov was quoted as saying by Interfax news agency.

He said Moscow had rejected as "unfounded" concerns raised by Washington over the situation.

The comments followed a telephone call on Friday in which Biden reassured his Ukrainian counterpart, Volodymyr Zelenskyy, of “unwavering support” in Ukraine’s confrontation with Russia-backed separatists holding parts of the eastern Donbas region.

Russia on Monday denied that Russian military movements posed a threat to Ukraine and dismissed fears of an expansion 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”.

Last week, the NATO alliance also expressed concern over what is said was a large Russian military buildup on Russia’s side of the border with eastern Ukraine.

For his part, Zelenskiy has accused Russia of whipping up tensions.

“Muscle-flexing in the form of military exercises and possible provocations along the border is a traditional Russian affair,” the Ukrainian president said in a statement on April 1.

Ukraine, Western countries and NATO accuse Russia of sending troops and heavy weapons to prop up its proxies in Donbas in 2014. (rt/ez)