U.S. President Joe Biden expressed "deep concern" over Russia's military buildup near the Ukraine border in a videoconference with his Russian counterpart Vladimir Putin on Tuesday, and warned of a strong response from his country and its European allies in the event of a military escalation, the White House said.
The move comes as tensions are mounting over a potential Russian military invasion of Ukraine following Moscow's annexation of Crimea in 2014, with Washington assessing that Putin is "putting in place the capacity" to engage in further military escalation should he decide to do so.
The two-hour video call did not result in any breakthrough, Kremlin aide Yuri Ushakov told reporters after the summit, according to Russia's TASS news agency. Putin criticized NATO for beefing up its military capabilities near the Russian border.
Biden, for his part, "reiterated his support for Ukraine's sovereignty and territorial integrity" and called for de-escalation, the White House said.
He also made clear the United States and its European allies would respond with "strong economic and other measures in the event of military escalation," it said.
National Security Adviser Jake Sullivan told a press conference later in the day the Biden administration is prepared to implement economic sanctions that were eschewed in the wake of the Crimea annexation.
The "other measures" would include providing additional defensive materiel to Ukraine and fortifying NATO allies located near Russia with additional deployment of assets and capabilities, he said.
On the question of whether the United States is prepared to deal with a nightmare scenario of a Russian invasion of Ukraine and simultaneous Chinese aggression towards Taiwan, Sullivan said the United States is taking measures to prevent any such situation.
"The United States is going to take every action that we can take, from the point of view of both deterrence and diplomacy, to make sure that the Taiwan scenario...never happens and to try to avert the invasion and deter the invasion into Ukraine. That is the object of our policy right now," he said.
Media reports have cited U.S. intelligence indicating the possibility of a massive military offensive by Russia in Ukraine involving 175,000 troops as soon as early next year.
Putin, for his part, sought a guarantee from Washington that the North Atlantic Treaty Organization will not expand further eastwards, according to the Kremlin, apparently referring to moves to bring Ukraine into the alliance.
The United States has supported Ukraine becoming a NATO member while the alliance has also provided training to Ukrainian service members and advised Ukrainian officials on ways to improve their capabilities, according to the U.S. Defense Department.
Biden and Putin also discussed during the call a range of bilateral and regional issues, including dialogue between Washington and Moscow on strategic stability and ransomware, and Iran's nuclear ambitions, the White House said.
Biden and Putin previously held a face-to-face meeting in June and spoke on the phone the following month.
Biden said at the outset of Tuesday's meeting that he would like to meet Putin in person again, since they were unable to get together at the Group of 20 summit in late October in Italy.
The annexation of Crimea resulted in Russia's departure from the then Group of Eight major economies with Britain, Canada, France, Germany, Italy, Japan and the United States as well as the European Union.
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