WASHINGTON (AP) – Face to face for more than 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 an invasion of Ukraine would bring enormous harm to the Russian economy. The highly anticipated call between the two leaders came amid growing worries by the U.S. and Western allies about Russia’s threat to neighboring Ukraine.

Putin came into the meeting seeking guarantees from Biden that the NATO military alliance will never expand to include Ukraine, which has long sought membership. The Americans and their NATO allies said in advance that Putin’s request was a non-starter.

Biden “told President Putin directly that if Russia further invades Ukraine, the United States and our European allies would respond with strong economic measures,” U.S. National Security Adviser Jake Sullivan said.

He added that Biden said the U.S. would also “provide additional defensive material to the Ukrainians above and beyond that, which we are already providing, and we would fortify our NATO allies on the eastern flank with additional capabilities in response to such an escalation.”

Sullivan said that could include additional deployments of U.S. troops to eastern European NATO allies. “As we pursue diplomatic channels, we will also prepare for all contingencies,” he said.

As the U.S. and Russian presidents conferred, Ukrainian officials grew more anxious about the tens of thousands of Russia troops that have been deployed near 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 a potential invasion.

U.S. intelligence officials haven’t been able to independently verify that accusation, according to an administration official who spoke on the condition of anonymity to discuss the sensitive matter. But the official said the White House has directly raised concerns with the Russians about “resorting to their old playbook” by trying to provoke the Ukrainians.

Kremlin spokesman Dmitry Peskov refused to comment on the allegations, redirecting questions to Russia’s Defense Ministry, which had no immediate comment.

In a brief snippet from the start of the meeting broadcast by Russia state-run television, the two leaders offered friendly greetings to each other. “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 noted Putin’s absence from the recent Group of 20 summit in Rome. The Russian took part in the major gathering of industrial nations by video link because of concerns about COVID-19 at home.

“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 made clear that his administration stands ready to take actions that would exact “a very real cost” on the Russian economy, according to White House officials.

The Kremlin in its readout described the call as “candid and businesslike.”

“Putin emphasized that it’s wrong to put the responsibility on Russia, since it is NATO that has been making dangerous attempts to expand its presence on the Ukrainian territory and has been expanding its military potential near Russian borders,” the Kremlin said.

The Kremlin said the Russian leader also proposed to lift all mutual restrictions on diplomatic missions and help normalize other aspects of bilateral relations.

The leader-to-leader conversation – Biden speaking from the White House Situation Room, Putin from his residence in Sochi —was one of the toughest of Biden’s presidency and came 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.

Sullivan, speaking after the call, said the U.S. believes that Putin has not made a final decision to invade.

Biden was vice president in 2014 when Russian troops marched into the Black Sea peninsula of Crimea and annexed the territory from Ukraine. Aides said the Crimea episode – one of the darker moments for then-President Barack Obama on the international stage – looms large as Biden eyes the current crisis.

Poland, Hungary and the Czech Republic were formally invited in 1997 and joined in 1999. They were followed in 2004 by Bulgaria, Romania, Slovakia, Slovenia and the former Soviet states of Estonia, Latvia and Lithuania. Since then, Albania, Croatia, Montenegro and North Macedonia have joined, bringing NATO’s total to 30 nations.

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 Republicans said 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 Monday. “And President Biden has an opportunity to set the tone when he speaks with Putin.”

Trump 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.