Face to face for just over two hours, President Joe Biden and Russia’s Vladimir Putin squared off in a secure video call Tuesday as the U.S. president put Moscow on notice that a Russian invasion of Ukraine would bring enormous harm to the Russian economy.

The call was highly anticipated and came amid increasing fears by the U.S., western allies about a Russian invasion in neighboring Ukraine. Putin sought assurances from Biden to ensure that NATO’s military alliance would never be expanded to include Ukraine. Ukraine has been seeking membership for many years. The Americans and their NATO allies said in advance that Putin’s request was a non-starter.

The U.S.-Russian presidents met and became increasingly concerned by the thousands of Russian troops deployed close to their border.

Just hours before the start of the Biden-Putin video call, Ukrainian officials charged Russia had further escalated the smoldering crisis by sending tanks and snipers to war-torn eastern Ukraine to “provoke return fire” and lay a pretext for the potential invasion.

Kremlin spokesman Dmitry Peskov refused to comment on the allegations, redirecting questions to Russia’s Defense Ministry, which hasn’t made any immediate comment.

Russia’s state television broadcast a short excerpt from the opening of the meeting. It showed the leaders greeting each other in friendly greetings before they began what was expected to be a lengthy discussion.

“I welcome you, Mr. President,” Putin said, speaking with a Russian flag behind him and a video monitor showing Biden in front of him.

“Good to see you again!” Biden replied with a chuckle. He then quickly noted Putin’s absence from the recent Group of 20 summit in Rome.

Because of domestic concerns over Covid-19, the Russian participant in the largest gathering of industrial countries via video link was unable to attend.

“Unfortunately, last time we didn’t get to see one another at G-20,” Biden said. “I hope next time we meet to do it in person.”

Biden aimed to make clear that his administration stands ready to take actions against the Kremlin that would exact “a very real cost” on the Russian economy, according to White House officials. Putin, for his part, was expected to demand guarantees from Biden that the NATO military alliance will never expand to include Ukraine, which has long sought membership. That’s a non-starter for the Americans and their NATO allies.

“We’ve consulted significantly with our allies and believe we have a path forward that would impose significant and severe harm on the Russian economy,” White House press secretary Jen Psaki said Monday in previewing the meeting. “You can call that a threat. That can be called a fact. It can also be called preparation. You can call it whatever you want to call it.”

The leader-to-leader conversation — Biden speaking from the Situation Room, Putin from his residence in Sochi —was one of the toughest of Biden’s presidency and comes at a perilous time. U.S. intelligence officials have determined that Russia has massed 70,000 troops near the Ukraine border and has made preparations for a possible invasion early next year.

Although the U.S. is not certain if Putin made an ultimatum to invade, it hasn’t been determined by them. Still, Biden sought to make clear to the Russian leader that there will be a “very real cost” should Russia proceed with military action, according to a senior administration official who briefed reporters on the condition of anonymity.

Biden was vice president in 2014 when Russian troops marched into the Black Sea peninsula of Crimea and annexed the territory from Ukraine. Aides say the Crimea episode — one of the darker moments for former President Barack Obama on the international stage — looms large as Biden looks at the current smoldering crisis.

Since its inception, the eastward expansion NATO has been an issue of dispute not only with Moscow but also within Washington. In 1996, when President Bill Clinton’s national security team debated the timing of membership invitations to former Soviet allies Poland, Hungary and the Czech Republic, Defense Secretary William Perry urged delay to keep Russian relations on track. Perry stated in his memoirs that he thought about resigning after losing the internal discussion.

The Czech Republic, Hungary, Poland and Hungary were officially invited to join the European Union in 1997. In 2004, they were joined by Bulgaria, Romania and Slovakia as well as Slovenia, Slovenia, and former Soviet countries of Estonia, Latvia, and Lithuania. Since then, Albania, Croatia, Montenegro and North Macedonia have joined, bringing NATO’s total to 30 nations.

NATO’s core principle is that any country can apply for membership. No outsider can have a membership veto. While there’s little prospect that Ukraine would be invited into the alliance anytime soon, the U.S. and its allies won’t rule it out.

In Washington, Republicans are framing this moment as a key test of Biden’s leadership on the global stage. Biden vowed as a candidate to reassert American leadership after President Donald Trump’s emphasis on an “America first” foreign policy. But Biden has faced fierce criticism from Republicans who say that he’s been ineffective in slowing Iran’s march toward becoming a nuclear power and that the Biden administration has done too little to counter autocratic leaders like China’s Xi Jinping, Iran’s Ayatollah Ali Khamenei and Putin.

“Fellow authoritarians in Beijing and Tehran will be watching how the free world responds,” Senate Minority Leader Mitch McConnell said from the Senate floor on Monday. “And President Biden has an opportunity to set the tone when he speaks with Putin.”

Trump, who showed unusual deference to Putin during his presidency, said in a Newsmax interview on Monday that the Biden-Putin conversation would not be a “fair match,” describing it as tantamount to the six-time Super Bowl champion New England Patriots facing a high school football team.

Biden spoke Monday with the leaders of France, Germany, Italy, and the United Kingdom to discuss possible sanctions and messaging. After his meeting with Putin, Biden scheduled to talk with them once again Tuesday. His goal is to work with allies and to avoid imposing additional sanctions on Russia.

On Monday, Antony Blinken, Secretary of State of Ukraine, spoke to Volodymyr Zelenskyy about the Biden-Putin confrontation.

Zelenskyy wrote on Twitter that he and Blinken “agreed to continue joint & concerted action” and expressed his gratitude for the U.S. and allies providing “continued support of our sovereignty & territorial integrity.” Biden is expected to speak with Zelenskyy later this week.

State Department spokesman Ned Price said that Blinken “reiterated the United States’ unwavering support for Ukraine’s sovereignty, independence, and territorial integrity in the face of Russian aggression.”

The Kremlin has made clear that Putin planned to seek binding guarantees from Biden precluding NATO’s expansion to Ukraine. Biden and aides have indicated no such guarantee is likely, with the president saying he “won’t accept anyone’s red line.”

Psaki stressed “NATO member countries decide who is a member of NATO, not Russia. And that is how the process has always been and how it will proceed.”

Putin still sees it as an opportunity to adjust the power dynamics of the U.S.-Russian relationship.

“It is about fundamental principles established 30 years ago for the relations between Russia and the West,” said Fyodor Lukyanov, a leading Moscow-based foreign policy expert. “Russia demands to revise these principles, the West says there’s no grounds for that. So, it’s impossible to come to an agreement just like that.”

Other than Ukraine, many other important issues are on the agenda, such as cyberattacks or human rights. Kremlin spokesman Dmitry Peskov said U.S.-Russian relations are overall in “a rather dire state.”

The White House and Kremlin both sought to reduce expectations ahead of the call. Both sides said they didn’t expect any breakthroughs on Ukraine or the other issues up for discussion, but that just the conversation itself will be progress.

Kremlin spokesperson Dmitry Peskov told reporters Tuesday that “obviously, if the two presidents decided to have a conversation, they intend to discuss issues and don’t mean to bring matters to a dead end.”

“Putin has repeatedly said that we look for good, predictable relations with the U.S.,” Peskov said. “Russia has never planned to attack anyone. But we have our own concerns, our own red lines — the president spoke clearly about that. To that, Mr. Biden responded that he doesn’t intend to accept any red lines. This issue will be discussed (during the call) as well.”

Peskov characterized the Biden-Putin call as a “working conversation during a very difficult period,” when “escalation of tensions in Europe is off the scale, extraordinary.”