President Joe Biden told Kremlin leader Vladimir Putin the US stood by its “unwavering” support for Ukraine in defending its territory against a build-up by Russian troops, as tension between the superpowers skyrockets.

Ukraine said on Monday that the Kremlin was not responding to its request from President Volodymyr Zelensky for talks on heightened tension along the neighbours’ border and suggested that Russia might be funnelling even more troops next to areas of the country held for seven years by separatists aligned with Moscow.

Ukrainian President Volodymyr Zelensky’s press secretary has reopened a highly divisive debate over the use of the Russian language in the country, saying that alongside Ukrainian there existed “Ukrainian Russian” as a fundamental part of national identity.

A mark of the seriousness with which Washington regards Russia’s sudden troops build up on Ukraine’s border is that, after months of silence, it provoked new President Joe Biden’s first telephone conversation with Ukrainian President Volodymyr Zelensky.

The White House is in talks to appoint a special envoy to lead negotiations on halting the construction of Russia-to-Germany gas pipeline Nord Stream 2, current and former U.S. officials said, as the Biden administration grapples with how to stymie a nearly completed energy project that would serve as a major financial and geopolitical boon to Moscow, POLITICO reported.