US President Joe Biden on Saturday warned his Russian counterpart Vladimir Putin of dire consequences if an invasion of Ukraine takes place.

Biden’s warning came in a high-stakes telephone call between the two heads of state over the tense situation in Ukraine. The call started at 11.04 ET and lasted a little over an hour.

“President Biden spoke with President Vladimir Putin today to make clear that if Russia further invades Ukraine, the U.S. and our allies will impose swift and severe costs on Russia,” said the White House in a statement shortly after the call.

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The White House added that Biden advised his Russian counterpart to take diplomatic means instead of resorting to a show of force, saying, “President Biden urged President Putin to engage in de-escalation and diplomacy instead.”

The telephone call between Biden and Putin marked the first time they had spoken since the turn of the year. The two first met face-to-face in Geneva in June 2021, and had two phone conversations in December 2021.

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The call came hours after the US ordered its embassy staff in Ukraine to evacuate the country at the earliest, amid reports of further Russian troop build-up along areas in western Russia, Belarus, and Crimea.

Ukraine has also alleged that Russia has blockaded the Black Sea and the Sea of Azov, cutting of sea-based access to the country.

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Given the troop build-up along Ukraine’s borders, US officials have said that an invasion could take place any time, even before the end of the Beijing 2022 Winter Olympics on February 20.

Russia, for its part, maintains that it has no intentions of invading Ukraine and are merely seeking security guarantees. Moscow has also accused Washington and its NATO allies of running a misinformation campaign against Russia.

“At the end of 2021 and the beginning of 2022, the global information space faced a media campaign unprecedented in its scale and sophistication, the purpose of which is to convince the world community that the Russian Federation is preparing an invasion of the territory of Ukraine,” the Russian Ministry of Foreign Affairs said in a statement.