US President Joe Biden on Tuesday urged Russian counterpart Vladimir Putin to ease mounting tensions with Ukraine and proposed a summit between the two leaders in a third country.

In a phone call with Putin, Biden "voiced our concerns over the sudden Russian military build-up in occupied Crimea and on Ukraine's borders, and called on Russia to de-escalate tensions," a White House statement said.

"President Biden reaffirmed his goal of building a stable and predictable relationship with Russia consistent with US interests, and proposed a summit meeting in a third country in the coming months to discuss the full range of issues facing the United States and Russia."

The summit would between the first between Putin and Biden, who took office vowing a tougher line on Russia including over its alleged interference in US elections and harsh treatment of ailing opposition leader Alexei Navalny.

Putin similarly held a summit in Finland in 2018 with then US president Donald Trump, who caused a furor at home by appearing to accept the Russian leader's denials of election meddling.

Tensions have soared in recent days over Russian movements at the Ukrainian border, with the United States saying that troop levels are at their highest since 2014 when war first broke out with Moscow-backed separatists.

Russia earlier Tuesday announced additional trips in "training exercises" as it described itself as threatened by NATO actions.

It came as Ukrainian Foreign Minister Dmytro Kuleba met in Brussels with top officials of NATO nations including Secretary of State Antony Blinken, who voiced his strong support for Kiev.