US president Joe Biden and Russian counterpart Vladimir Putin will speak in a video call on Tuesday as tensions escalate over a Russian troop build-up on the Ukrainian border – seen as a sign of a potential invasion.

Kremlin spokesman Dmitry Peskov confirmed plans on Saturday for the much-anticipated call and said it will take place in the evening.

Russia is adamant that the US should guarantee that Ukraine will not be admitted to the Nato military alliance.

US intelligence officials, meanwhile, have determined that Russia has massed about 70,000 troops near its border with Ukraine and has begun planning for a possible invasion as soon as early next year, according to a Biden administration official.

The risks for Mr Putin of going through with such an invasion would be enormous.

Vladimir Putin
Russian president Vladimir Putin (Kremlin Pool Photo via AP)

US officials and former American diplomats say while the Russian president is clearly laying the groundwork for a possible invasion, Ukraine’s military is better armed and prepared today than in the past, and that sanctions threatened by the West would do serious damage to the Russian economy.

Mr Biden said on Friday: “What I am doing is putting together what I believe to be, will be, the most comprehensive and meaningful set of initiatives to make it very, very difficult for Mr Putin to go ahead and do what people are worried he may do.”

Ukrainian officials have said Russia could invade next month.

Ukraine Russia
Ukrainian soldiers walks under a camouflage net in a trench on the line of separation from pro-Russian rebels near Debaltsevo, Donetsk region, Ukraine (AP)

The country’s defence minister, Oleksii Reznikov, said the number of Russian troops near Ukraine and in Russia-annexed Crimea is estimated at 94,300, and warned that a “large-scale escalation” is possible in January.

Ukraine’s president, Volodymyr Zelenskyy, recently charged that a group of Russians and Ukrainians planned to attempt a coup in his country and that the plotters tried to enlist the help of Ukraine’s richest man, Rinat Akhmetov.

Russia and Mr Akhmetov have denied that any plot is under way, but the Russians have become more explicit recently in their warnings to Ukraine and the United States.

Volodymyr Zelenskyy
Ukrainian president Volodymyr Zelenskyy (AP)

Mr Biden is tentatively also scheduled to speak with Mr Zelenskyy in the coming week, according to a person close to the Ukrainian leader.

The Kremlin said on Friday that Mr Putin, during his call with Mr Biden, would seek binding guarantees precluding Nato’s expansion to Ukraine.

Mr Biden tried to head off the demand in comments to reporters on Friday before leaving for a weekend stay at Camp David.

“I don’t accept anyone’s red line,” Mr Biden said.

White House press secretary Jen Psaki said the US administration would coordinate with European allies if it moved forward with sanctions.

Jen Psaki
White House press secretary Jen Psaki (AP)

She alluded to Russia’s 2014 annexation of Crimea, the Black Sea peninsula that had been under Ukraine’s control since 1954.

Russia has also backed separatists in eastern Ukraine in a seven-year conflict that has cost more than 14,000 lives.

“We know what President Putin has done in the past,” Ms Psaki said. “We see that he is putting in place the capacity to take action in short order.”

US-Russian relations have been rocky since Mr Biden took office.

His administration has imposed sanctions against Russian targets and called out Mr Putin for the Kremlin’s interference in US elections, cyberactivity against American companies and the treatment of opposition figure Alexei Navalny, who was poisoned last year and later imprisoned.

When Mr Putin and Mr Biden met in Geneva in June, Mr Biden warned that if Russia crossed certain red lines – including going after major American infrastructure – his administration would respond and “the consequences of that would be devastating”.