MOSCOW (AP) — President Joe Biden and Russian President Vladimir Putin will speak in a video call Tuesday as tensions between the U.S. and Russia escalate over a Russian troop buildup on the Ukrainian border seen as a sign of a potential invasion.

Kremlin spokesman Dmitry Peskov confirmed plans on Saturday to Russia’s state news agency RIA Novosti and said it will take place in the evening. Peskov added that “the presidents will decide themselves” how long the conversation will last.

White House did not immediately comment on the announcement.

Russia is more adamant than ever that the U.S. guarantees that Ukraine will not be admitted to the NATO military alliance. U.S. 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 who was not authorized to discuss that finding publicly and spoke on the condition of anonymity.

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

U.S. 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.

“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,” Biden said Friday.

Ukrainian officials have said Russia could invade next month. Ukraine’s defense 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 Akhmetov have denied that any plot is underway, but the Russians have become more explicit recently in their warnings to Ukraine and the United States.

Biden is tentatively also scheduled to speak with Zelenskyy in the coming week, according to a person close to the Ukrainian leader. This person was not authorized to comment publicly before the announcement of the call and spoke on the condition of anonymity.

The Kremlin said Friday that Putin, during his call with Biden, would seek binding guarantees precluding NATO’s expansion to Ukraine. Biden tried to head off the demand in comments to reporters Friday before leaving for a weekend stay at Camp David.

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

White House press secretary Jen Psaki said Friday that the administration would coordinate with European allies if it moved forward with sanctions. 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 7-year conflict that has cost over 14,000 lives.

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

U.S.-Russia relations have been rocky since Biden took office.

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

When Putin and Biden met in Geneva in June, 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.”

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