“I have made it clear to President Putin that we will take tough sanctions and that we will increase our presence in Europe, among our NATO allies,” the US president said, after being questioned on Friday in his telephone interview with Mr. Putin.

“We were clear: He can’t, I repeat, he can’t invade Ukraine,” he told reporters at the exit of a restaurant in Wilmington, Delaware where he was passing with his family for year-end festivities.

For his part, the Russian President said that the new sanctions against Moscow would be a “fatal mistake.”

After this 50-minute phone conversation – the second in less than a month – the two men nonetheless praised the diplomatic path out of the crisis.

A White House official said Biden will reaffirm to Ukraine’s president on Sunday “U.S. support for Ukraine’s independence and territorial integrity.”

The official added that Joe Biden “will discuss Russia’s military deployment on Ukraine’s borders and review preparations for upcoming diplomatic meetings aimed at reducing tension in the region.”

Volodymyr Zelensky said on Twitter that he was impatient for the US president to discuss “ways to coordinate our actions in the interests of peace in Ukraine and security in Europe.”

Meanwhile, Foreign Minister Anthony Blinken announced that he had called NATO Secretary General Jens Stoltenberg on Friday. In a tweet, the head of US diplomacy called on Russia to “get seriously involved” in negotiations aimed at allowing tensions over Ukraine to de-escalate.

Kiev and its Western allies accuse Moscow of massing tens of thousands of troops on the country’s borders in anticipation of a possible invasion.

Mr Stoltenberg wrote on Twitter that NATO was “united” and “ready for dialogue”.

The United States and Russia are scheduled to hold talks on Ukraine from January 10-11 in Geneva. Led by US Deputy Secretary of State Wendy Sherman and her Russian counterpart Sergei Ryabkov, they will be followed on January 12 by a meeting between Russia and NATO, and then on January 13 by a meeting within the framework of the Organization for Security and Cooperation in Europe.

The United States, accused of leading some international issues without paying much attention to its allies, insists precisely on close coordination with Europeans and Ukrainians.

Russia, which already annexed part of Crimea in 2014, is also widely regarded as the godfather of pro-Russian separatists in the conflict that has been tearing the country’s east for nearly eight years.