American President Joe Biden will have a phone call with his Russian counterpart, Vladimir Putin, on Thursday afternoon as international concern grows that Russia will invade Ukraine.

“The call was requested by Putin, according to an administration official, and Biden accepted because ‘he believes when it comes to Russia there is no substitute for direct leader-leader dialogue,'” reports CNN.

The U.S. and Russia have already scheduled security talks for Jan. 10.

In recent months, Russia has amassed as many as 120,000 troops on its border with Ukraine. Foreign Policy writes that the soldiers are in a state of “battlefield readiness that military analysts say gives Moscow the capability to launch an offensive with little prior warning.”

The outlet adds:

Fueling its readiness to act are deep-rooted Russian grievances over the eastward expansion of NATO and the weapons supplied by the alliance to Ukraine, which Putin sees as historically Russian but which is slipping rapidly out of his grasp.

At a recent press conference, Putin expressed resentment of the close relationship between the U.S. and Ukraine, saying, “It was the United States that came with its missiles to our home, to the doorstep of our home.” 

The U.S. and its allies “must understand that we have nowhere to retreat further” Putin said.

He added that Moscow will take “adequate military-technical measures” if the U.S. continues its “aggressive” course.

Ukraine has sought NATO membership for years, which Russia considers a provocation.

Earlier this month, Russia proposed a diplomat agreement with the U.S. and other NATO members “that would bar the alliance from expanding to include Ukraine or other countries in the post-Soviet region that are not yet members, or conducting any military activity there,” according to The New York Times.

NATO rejected the proposal. U.S. National Security Advisor Jake Sullivan said recently that Biden “stands by the proposition that countries should be able to freely choose who they associate with.”

The Associated Press reports:

Secretary of State Antony Blinken spoke on Wednesday with Ukrainian President Volodymyr Zelenskyy.

State Department spokesman Ned Price said Blinken “reiterated the United States’ unwavering support for Ukraine’s independence, sovereignty, and territorial integrity in the face of Russia’s military buildup on Ukraine’s borders.”

Biden and Putin held a video conference on December 7th. Biden threatened strong economic sanctions if Putin decided to invade his neighbor.

The Washington Post provides key context:

The tension comes against the backdrop of a conflict in Ukraine’s eastern Donbas region, which has been simmering for nearly eight years and, according to Ukraine, has left more than 14,000 people dead. Russia fueled a separatist rebellion in the region in 2014 after pro-Western demonstrators toppled a Kremlin-friendly government in Kyiv and took power.