Joe Biden has called on Russian president Vladimir Putin to de-escalate tensions at the Ukraine-Crimea border, where he has been amassing troops since March.
There are more Russian troops on the border of Ukraine than there were ahead of Russia's invasion and eventual annexation of Crimea in 2014, according to the White House.
Mr Biden and Mr Putin spoke on the phone about “a number of regional and global issues”, according to a White House synopsis of the call.
Among topics the two discussed was the future of Russian and American arms agreements branching off the New Start (Strategic Arms Reduction) Treaty.
When the pair talked about security issues, Mr Biden reportedly told Mr Putin the US would not tolerate further interference in its elections or other cyber incursions.
He reportedly also said he wanted to normalise relations between the countries, suggesting a summit in a third country where the two presidents could meet and talk.
Despite calls for less aggressive posturing between the two countries, the border issue remains a point of stark contention between them.
Mr Biden reportedly told Mr Putin that the US had “unwavering commitment to Ukraine’s sovereignty and territorial integrity”.
Ukrainian officials claim there are 50,000 Russian troops along Russia's western border and in Crimea, which accounts for 18 per cent of the country’s entire ground force.
Global affairs analyst Michael Bociurkiw said in a CNN op-ed that Russia’s build-up was unlikely to be a precursor to an invasion of Ukraine due to the likelihood of significant casualties during the muddy season, but may instead be a means of pressuring Ukraine to implement the 2015 Minsk framework.
If adopted, it would provide a “special status” to the regions of Luhansk and Donetsk, granting them greater autonomy in exchange for a permanent ceasefire between the countries.
He also suggested that the build-up could be meant as a means of testing Mr Biden’s mettle, sending him the message that Russia still considers Ukraine part of its sphere of control, despite the country's ties with Nato.
Ukraine is not a member of Nato, but its president, Volodymyr Zelensky, has called for Nato to implement a membership action plan for the country.
