Ukrainian President Volodymyr Zelenskiy spoke to U.S. Secretary of State Antony Blinken by phone on December 6 ahead of President Joe Biden’s call with Russian President Vladimir Putin in which Biden is expected to issue a strong warning against a Russian invasion of Ukraine.
"Agreed to continue joint & concerted action. Grateful to U.S. strategic partners & allies for the continued support of our sovereignty & territorial integrity," Zelenskiy said on Twitter.
Russia's troop buildup as well as Ukraine's efforts to join the NATO alliance are expected to top the agenda of the video call between Biden and Putin on December 7.
Biden will make clear to Putin that there will be "very real costs" should Russia choose to proceed with military aggression against Ukraine, a White House official said in a background briefing call with reporters.
There "will be genuine and meaningful and enduring costs to choosing to go forward,” the official said.
The United States and European allies are prepared to take "substantial economic countermeasures...that would impose significant and severe economic harm on the Russian economy" if Russia attacks, the official said.
Ukraine has accused Russia of massing tens of thousands of troops near its border in preparation for a possible major military offensive. Russia has dismissed talk of a new assault on Ukraine as fearmongering and describes relations between the United States and Russia as in “a lamentable state.”
U.S. intelligence reports have suggested that Russia could be preparing to invade Ukraine as early as 2022. Russia seized Ukraine's Crimean Peninsula in 2014 and backs separatists in eastern Ukraine who have waged a bloody war against Kyiv that began the same year.
Moscow has demanded written guarantees that Ukraine will not be allowed to join NATO, calling such a scenario a "red line." The Kremlin has also expressed concerns about Western weapons supplies to Kyiv, as well as military drills in international waters of the Black Sea.
NATO and Ukraine, a former Soviet republic, have had friendly relations since the country gained its independence in the early 1990s. The two have deepened their cooperation since Russia's military actions in Ukraine in 2014.
Ukraine adopted legislation in 2017 reiterating its aim to join NATO as a strategic objective. However, Zelenskiy this summer expressed frustration over the issue, calling on Biden to give Kyiv either a "yes" or "no" on mapping out a plan for Ukraine to enter the alliance.
The United States has provided more than $2.5 billion in security assistance to Ukraine since 2014, and both Washington and NATO have offered assurances of their unwavering support for Ukraine in the face of Russian aggression.
Regarding Moscow's ultimatums, Biden has said that he will not accept "anyone's red line."
Biden and Putin have met as presidents in person once, in Geneva in June. They last spoke by telephone in July.