Ukrainian and Western officials have worried about a Russian troop build-up near Ukraine, saying it could signal Moscow's intention of an attack.

Russian diplomats countered those claims by expressing concern about Ukraine's own military build-up near the area of the separatist conflict in the eastern part of the country.

US Secretary of State Antony Blinken, noting Putin could quickly order an invasion of Ukraine, warned Washington stood ready to inflict heavy sanctions on Russia if he did.

Speaking at a Kremlin ceremony where he received credentials from foreign ambassadors on Wednesday, Putin emphasised Russia would seek "reliable and long-term security guarantees".

"In a dialogue with the United States and its allies, we will insist on working out specific agreements that would exclude any further NATO moves eastward and the deployment of weapons systems that threaten us in close vicinity to Russian territory," Putin said.

He charged that "the threats are mounting on our western border", with NATO placing its military infrastructure closer to Russia and offered the West to engage in substantive talks on the issue, adding Moscow would need not just verbal assurances, but "legal guarantees".

Putin's statement came a day after he sternly warned NATO against deploying its troops and weapons to Ukraine, saying it represented a red line for Russia and would trigger a strong response.

Tensions have been soaring in recent weeks about a Russian troop build-up near Ukraine, which worried Ukrainian and Western officials, who saw it as a possible sign of Moscow's intention to invade its former Soviet neighbour.

NATO foreign ministers warned Russia on Tuesday that any attempt to further destabilise Ukraine would be a costly mistake.

Australian Associated Press