(Bloomberg) -- President Joe Biden will reaffirm U.S. support for Ukraine’s sovereignty in the face of a Russian military buildup when he holds a video call with President Vladimir Putin on Tuesday, according to a White House statement.

The diplomatic effort, which the Kremlin announced earlier Saturday, follows weeks of escalating tension over Russian encroachment on its neighbor. A senior administration official said Friday that U.S. intelligence had concluded the Kremlin was planning an offensive against Ukraine as soon as next year involving an estimated 175,000 personnel.

“President Biden will underscore U.S. concerns with Russian military activities on the border with Ukraine and reaffirm the United States’ support for the sovereignty and territorial integrity of Ukraine,” White House spokeswoman Jen Psaki said in the statement.

Biden said Friday he anticipates a “long discussion” with Putin about the threat of an invasion of Ukraine, and dismissed the Russian leader’s warning that deployment of Western weapons or troops represented a “red line.” 

Defense Secretary Lloyd Austin said Saturday it’s vital that Ukraine have the resources needed to defend itself, though he declined to specify what kind of additional aid the U.S. might provide to Ukraine’s military. He also said there is still an opportunity to defuse the situation.

“I think there’s a lot of space here for diplomacy and leadership to work and, again, we’re going to remain engaged with our allies in the region and our partners in the region,” Austin said during a security forum at the Ronald Reagan Presidential Library in Simi Valley, California. “We’re going to continue to do everything we can to help provide Ukraine the capability to protect its sovereign territory.”

Putin’s deployment of as many as 100,000 troops and military equipment on Ukraine’s border has revived fears of war first raised in the spring, when the Russian leader made similar moves. While those tensions subsided following an April call between Biden and Putin, U.S. officials have recently shared intelligence with allies showing that Putin could order a rapid, large-scale incursion into Ukraine from multiple locations. 

White House officials said Friday they were considering economic sanctions and security assistance to Ukraine in response to the Russian troop buildup. Biden said earlier Friday he was coordinating with allies in Europe to deter Putin from an attack.

“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 told reporters. 

The U.S. believes roughly half of the Russian units are already at the border and that Russian proxies and media outlets have increased the distribution of content denigrating Ukraine, according to the U.S. official, who requested anonymity to detail an internal intelligence assessment.

The tension played out at a meeting of the Organization for Security and Cooperation in Europe, where U.S. Secretary of State Antony Blinken and Russian Foreign Minister Sergei Lavrov had a testy exchange over Ukraine at a dinner on Wednesday with dozens of their colleagues, according to people familiar with the discussions.

Biden and Putin will also discuss strategic stability, cyber and regional issues, Psaki said.

©2021 Bloomberg L.P.