Media reports say U.S. President Joe Biden said he would consider personally sanctioning Vladimir Putin if he orders an invasion of Ukraine.  Meanwhile, Russia has reportedly accused the United States of “escalating tensions” over the issue and denies planning to enter Ukraine.

Tensions remained high after NATO said on Monday it was putting forces on standby and reinforcing Eastern Europe with more ships and fighter jets in response to a Russian troop build-up near its border with Ukraine.

Al Jazeera says Ukraine’s President Volodymyr Zelenskyy, in a televised video address on Tuesday evening, urged his compatriots to stay calm and said work was under way to bring about a meeting between him and the leaders of Russia, Germany and France.

“There are no rose-colored glasses, no childish illusions, everything is not simple … But there is hope,” he said.

The US and the European Union have threatened economic sanctions if Russia were to launch an invasion and Western leaders have said unity is paramount, though differences have emerged among European nations about how best to respond.

President Biden reportedly repeated on Tuesday that there were no plans to send US troops to Ukraine, which is not a NATO member. 

Taking questions from reporters, Mr. Biden replied “yes” when asked whether he could see himself imposing sanctions on the Russian president personally in the event of an invasion. 

Such a move across Ukraine's border would mean "enormous consequences worldwide" and could amount to “the largest invasion since World War II,” U.S. president said.

British Prime Minister Boris Johnson urged European allies to be ready to deploy sanctions as soon as there was an incursion.

Meanwhile, Russia has accused the US and others of "escalating tensions" over the issue and denies planning to enter Ukraine.  Moscow said it was watching with “great concern.”

However, Russia has deployed an estimated 100,000 soldiers near the border, according to the BBC.

The Kremlin has said it sees the Western military alliance NATO as a security threat, and is demanding legal guarantees that it will not add new members further east, including neighboring Ukraine.