Sullivan urges Russia to de-escalate

White House national security adviser Jake Sullivan encouraged Russia to de-escalate its troop buildup on the border with Ukraine in a phone call with his Russian counterpart on Monday.

Sullivan spoke with Yuri Ushakov, Russian President Vladimir Putin's foreign policy adviser, and "indicated U.S. readiness to engage in diplomacy through multiple channels, including bilateral engagement, the NATO-Russia Council, and the OSCE [Organization for Security and Cooperation in Europe]," according to a White House statement on the phone call.

"[Sullivan] made clear that any dialogue must be based on reciprocity and address our concerns about Russia's actions, and take place in full coordination with our European Allies and partners," the White House continued. "He also noted that substantive progress can only occur in an environment of de-escalation rather than escalation."

Sullivan has spoken with Ushakov twice in less than a week as the U.S. looks to ward off a Russian invasion of Ukraine. Russia has amassed tens of thousands of troops on the border with Ukraine, sparking concerns it could further invade after the 2014 seizure of Ukraine's Crimean Peninsula.

President Biden has threatened economic sanctions should Russia move to invade its neighbor. He also told Putin in a lengthy video call earlier this month that the U.S. would send additional security assistance to Ukraine and reinforcements to NATO's eastern flank were Russia to invade.

At the same time, Biden has ruled out sending U.S. forces into Ukraine.

Russia has demanded commitments from NATO that it not expand eastward to include Ukraine, but NATO officials have refused to rule out Ukraine and other countries in eastern Europe joining the alliance in the future. Russia has also characterized Ukraine and NATO as the aggressor, which U.S. officials say is the opposite of the truth.

Sullivan said last week that U.S. intelligence had assessed that Putin has not yet made up his mind on whether to invade Ukraine, but has laid the groundwork to do so if he chooses.