Biden warned Putin of 'substantive economic countermeasures' should he invade Ukraine

President Biden spoke with Russian President Vladimir Putin over a secure video call this morning in an attempt to de-escalate tensions between Russia and Ukraine – a key U.S. ally that U.S. officials have promised to defend – as Russian military forces continue to amass along the border with its neighbor.

The meeting began at 10:07 a.m. ET and pundits believe it may have been one of the most consequential foreign policy meetings of the Biden presidency to date, the New York Times reported.

According to a White House statement about the call, Biden "voiced the deep concerns of the United States and our European Allies about Russia's escalation of forces surrounding Ukraine and made clear that the US and our Allies would respond with strong economic and other measures in the event of military escalation."

He also "reiterated his support for Ukraine's sovereignty and territorial integrity and called for de-escalation and a return to diplomacy," the White House announced.

Biden is also said to have laid out which steps – including "substantive economic countermeasures" meant to inflict "significant and severe economic harm on the Russian economy" – the U.S. is prepared to take should the Kremlin decide to invade Ukraine.

In addition to discussing Ukraine, the two leaders reportedly discussed "the US-Russia dialogue on Strategic Stability, a separate dialogue on ransomware, as well as joint work on regional issues such as Iran."

Presently, the administration is also exploring options for an evacuation of U.S. citizens from Ukraine should Russian forces escalate the conflict, sources told CNN.

On Monday, Pentagon officials confirmed that U.S. intelligence has continued to observe increased Russian “military capability” along Ukraine's eastern border and in the annexed peninsula of Crimea.

U.S. Army Chief of Staff Gen. James McConville also noted that "somewhere around 95,000 to 100,000 Russian soldiers" were already posted on the Russian side of the border.

Sources familiar with the available intelligence have also noted that Russia has erected supply lines, including medical units and fuel, that could help sustain a drawn-out conflict.

"What we continue to see is added capability that President Putin continues to add, added military capability in the western part of his country and around Ukraine," Pentagon spokesman John Kirby said.

Ukrainian officials recently warned that Russia could invade as early as January – much like when it annexed the Crimean Peninsula in 2014.

“Our concern is that Russia may make the serious mistake of attempting to rehash what it undertook back in 2014, when it amassed forces along the border, crossed into sovereign Ukrainian territory and did so claiming — falsely — that it was provoked,” Secretary of State Antony Blinken said earlier this month. 

Although the Biden administration has no desire to send U.S. troops into battle, an escalation of conflict might force the U.S. to respond.

On Tuesday, skirmishes between Ukrainian soldiers and Russian-backed separatists began to break out along a roughly 250-mile-long barricade of trenches and fortifications.

The call between Biden and Putin concluded at 12:08 p.m. ET, and Jake Sullivan, Biden’s national security adviser, is expected to discuss the call with reporters at an afternoon press briefing.

Biden will have a follow-up call with the leaders of France, Italy, the U.K. and Germany on Tuesday afternoon.