US President Joe Biden and his Ukrainian counterpart Volodymyr Zelensky spoke about the alleged Russian military buildup along the border with Ukraine, and they both agreed they needed to pursue diplomacy and deterrence, the White House said in a readout of the call between the counterparts.

"The two leaders agreed on the importance of continuing to pursue diplomacy and deterrence in response to Russia's military build-up on Ukraine's borders," the White House added on the 50-minute call.

Biden also "made clear that the United States would respond swiftly and decisively, together with its allies and partners, to any further Russian aggression against Ukraine." 

Following the call, the Ukrainian president announced his conversation with Biden as well, saying he had discussed the current security situation, economic issues, sanctions, and alleged "Russian aggression" over the phone with his counterpart in Washington.

"Had an hour-long phone conversation with [US President Joe Biden]. Talked about security, economy, existing risks, sanctions, and Russian aggression. Details shortly," Zelensky wrote on Twitter.

Had an hour-long phone conversation with @POTUS @JoeBiden. Talked about security, economy, existing risks, sanctions and Russian aggression. Details shortly.

— Володимир Зеленський (@ZelenskyyUa) February 13, 2022

Biden had talked with Russian leader Vladimir Putin on Saturday, and the US president warned his Russian counterpart Washington would "respond decisively and impose swift and severe costs on Russia" should it, as he puts it, invade Ukraine.

The two presidents discussed Wahington's ideas on security in Europe; Putin said Russia would carefully consider Biden's ideas, though they do not deal with Russia's key concerns.

Russian Foreign Minister Sergey Lavrov said earlier these concerns included curbing NATO's expansion and the non-deployment of strike weapons systems near Russia's border, as Russia has been saying since the tensions started altogether.

The Pentagon confirmed Saturday that the US was removing nearly all of its remaining troops from Ukraine, as fears of a Russian invasion of the eastern European country rise.