United States President Joe Biden on Saturday told his Russian counterpart Vladimir Putin that Washington and its allies would “respond decisively” if Kremlin attacks Ukraine. US would impose swift and severe costs on Russia if Kremlin decides to attack its neighbour, Biden said.

“President Biden was clear with President Putin that while the United States remains prepared to engage in diplomacy…We are equally prepared for other scenarios,” the White House said in a press note about the hour-long call.

Biden also said that an invasion of Ukraine by Russia would result in “widespread human suffering”, according to the White House.

Demonstrators shout slogans as they stand with lit flares on a bridge with a banner 'Ukranians will resist - Say No to Putin' during a rally in Kyiv on February 12, 2022. | Sergei Supinsky/ AFP

Since early this year, Russia has amassed close to 1.3 lakh troops at the Ukrainian border, according to The New York Times. The two countries have been engaged in a conflict since 2014 when Russia annexed Ukraine’s Crimean Peninsula and backed separatist rebellions in the country’s eastern regions of Donetsk and Luhansk.

Russia has denied the speculation that it would invade Ukraine. However, Russia has asked for assurance from the member countries of the North Atlantic Treaty Organisation that the alliance’s military infrastructure deployment along the Ukrainian border will be scaled back, and that Ukraine will not be given a membership of the grouping.

Biden and Putin spoke on a day when the United States ordered most of its diplomats and other staff members to leave the American Embassy in Ukraine, The New York Times reported. Last week, it had urged its citizens in Ukraine to leave the country within 48 hours.

Apart from America, several other countries including Britain, Canada, Japan, Norway, New Zealand, and Denmark, have also asked their citizens to leave Ukraine.

Meanwhile, Russia said that on Saturday, it had chased off an American submarine from its territorial waters near the Kuril Islands in the northern Pacific region, AFP reported. Moscow alleged that the submarine had ignored demands to surface and fled at full speed after the Russian crew “used appropriate means”.

The United States military however denied the account, according to AFP.