President Joe Biden told Russian President Vladimir Putin during a video meeting on Tuesday that the United States "would respond with strong economic and other measures in the event of military escalation," the White House said, as Russia builds up its forces on its border with Ukraine.
"He told President Putin directly that if Russia further invades Ukraine, the United States and our European allies would respond with strong economic measures," Biden's top national security advisor, Jake Sullivan, said Tuesday of the call, which the White House said lasted two hours and one minute.
The meeting was "useful," and the discussion was "direct and straightforward," Sullivan told reporters.
"There was a lot of give and take," Sullivan said. "There was no finger wagging."
The call started at 10:07 a.m., according to the White House, and Russian TV showed Putin sitting at a long, wooden table looking at Biden on a TV monitor and the two men waving at each other.
"Welcome, Mr. President," Putin said.
"Hello. Good to see you again," Biden replied. "Unfortunately, last time we did not get to see each other at the G-20. I hope next time we meet we do it in person."
Putin spoke from his residence in the Russian resort city Sochi. Biden was in the White House Situation Room; the White House released a photograph showing him seated with Sullivan, Secretary of State Antony Blinken and Eric Green, a senior advisor on Russia.
During the meeting, the first conversation between the leaders since July, Biden told Putin that "we would provide additional defensive material to the Ukrainians, above and beyond that which we are already providing" and that the United States "would fortify our NATO allies on the eastern flank, with additional capabilities in response to such an escalation."
The United States already rotates relatively small contingents of American troops through Baltic countries as a symbolic measure.
"The question is what additional capabilities can we provide to ensure that they feel strong and confident in their own sovereignty and territorial integrity," Sullivan said. "It is those additional capabilities that are on the table in those countries should Russia move in Ukraine in -- in a more decisive way."
Sullivan would not provide more specifics about the economic measures with which he said Biden had threatened Putin.
"I will look you in the eye and tell you as President Biden looked President Putin in the eye and told him today that things we did not do in 2014, we are prepared to do now."
The president told ABC News White House correspondent MaryAlice Parks last week that "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."
After his call with Putin, the White House said, Biden spoke with France's President Emmanuel Macron, German Chancellor Angela Merkel, UK Prime Minister Boris Johnson and Italian Prime Minister Mario Draghi; the leaders had spoken the day before, too.
"The leaders underscored their support for Ukraine's sovereignty and territorial integrity," the White House said in a statement Tuesday, "as well as the need for Russia to reduce tensions and engage in diplomacy."
Biden planned to speak with Ukraine's President Volodymyr Zelenskyy on Thursday, the White House said.
A senior Biden administration official said Monday the U.S. was watching a series of events unfold similar to the lead-up to Russia's invasion of Ukraine in 2014, when it annexed the Crimean Peninsula. That included moving troops to its border with Ukraine coupled with a "significant spike" in anti-Ukrainian propaganda on social media, the official said.
But, Sullivan said Tuesday, the U.S. did not think Putin had decided yet if he would attack.
"We still do not believe that President Putin has made a decision," Sullivan said. "What President Biden did today was lay out very clearly the consequences if he chooses to move."
Ahead of the call, both the White House and Kremlin sought to lower expectations.
"It is very important not to have some overexcited, emotional expectations here," Putin spokesman Dmitry Peskov told Russia's Channel One on Monday.
Asked on Monday by ABC News White House correspondent Karen Travers if the White House's message was also to not have high expectations, White House press secretary Jen Psaki replied, "I think it is."
"The president is not going to hold back in conveying his concern," Psaki told another reporter.
Senate Minority Leader Mitch McConnell said Monday that Russia's "escalation" was "an immediate threat."
"The stakes for the president's call couldn't be clearer," McConnell said during remarks on the Senate floor.
In addition to Ukraine, Biden also spoke with Putin about strategic stability, ransomware and "joint work on regional issues such as Iran," the White House said.
The White House has made clear the U.S. is ready to support allies in the region if Russia decides to move forward with a military invasion in Ukraine.
Testifying before the Senate Foreign Relations Committee, the United States' under secretary of state for political affairs, Victoria Nuland, told Congress Tuesday that "this is a moment of testing."
"Both autocrats around the world and our friends around the world will watch extremely carefully what we do, and it will have implications for generations," Nuland said during testimony before the Senate Foreign Relations Committee.
After Russia invaded the Crimean Peninsula in 2014, the U.S. and the European Union leveled economic sanctions against Russia, and Russia was kicked out of the "Group of Eight" industrialized nations.
The United States also sent 600 troops to eastern Europe in a show of solidarity with Baltic nations on Russia's border. That deployment has morphed into a rotating set of relatively small U.S. deployments to eastern European nations.
The administration's preferred option for response to any Russian aggression would be a series of economic sanctions in concert with European partners, the official said, adding they would be "severe."
"We believe that we have a path forward that would involve substantial economic countermeasures by both the Europeans and the United States that would impose significant and severe economic harm on the Russian economy, should they choose to proceed. I'm not going to get into the specific details of that, but we believe that there is a way forward here that will allow us to send a clear message to Russia, that there will be genuine and meaningful and enduring costs to choosing to go forward should they choose to go forward with a military escalation in Ukraine," the official warned.
Blinken spoke with Ukraine's Zelenskyy on Monday ahead of Biden's call with Putin, and Zelensky tweeted that he had "agreed positions" with Blinken.
"Grateful to strategic partners & allies for the continued support of our sovereignty & territorial integrity," Zelensky wrote.
ABC News' Benjamin Siegel, Tanya Stukalova, Patrick Reevell, Shannon Crawford and Trish Turner contributed to this report.