US President Joe Biden and Russian President Vladimir Putin squared off in a secure video call Tuesday for more than two hours. The US president warned Moscow that an invasion of Ukraine would result in sanctions and significant economic damage to Russia.

With tens of thousands of Russian troops massed along the Ukraine border, the highly anticipated phone discussion between the two presidents occurred amid growing concern among the US and its Western allies over Russia's threat to its neighbor.

Putin, for his turn, approached Biden seeking assurances that NATO's military alliance would never expand to include Ukraine, which has long wanted membership. The Americans and their NATO allies declared that such a request was absurd.

There appeared to be no immediate progress toward de-escalating tensions over Ukraine. The US emphasized the importance of diplomacy and de-escalation while issuing stern warnings to Russia about the consequences of an invasion.

Biden "expressed directly to President Putin that if Russia invades Ukraine again, the US and our European allies will respond with strong economic measures," US National Security Adviser Jake Sullivan said following the call.

Additionally, he added, Biden stated that the US would "provide additional defensive material to the Ukrainians... and we would strengthen our NATO allies on the eastern flank with additional capabilities in response to such an escalation."

The adviser added that this might entail increased US troop deployments to NATO allies in eastern Europe.

Victoria Nuland, a senior US diplomat, said a Russian invasion of Ukraine would also threaten a contentious pipeline connecting Russia and Germany. She said Tuesday before the Senate Foreign Relations Committee that if Russia attacked, "our expectation is that the pipeline would be shut down."

During a conference call with reporters, Putin's foreign affairs adviser Yuri Ushakov rejected the possibility of penalties.

"While the US president discussed possible sanctions, our president stressed the importance of Russia's needs," Ushakov said. "Sanctions are not new; they have existed for a long period of time and will have no effect."

He described the presidents' video call as "frank and businesslike," noting that they occasionally traded jokes.

The two leaders exchanged pleasant greetings in a brief clip carried by Russia's national media.

"I greet you, Mr. President," Putin said, speaking in front of a Russian flag and a TV monitor showing Biden. "It's great to see you!" With a chuckle, Biden responded. He observed Putin's absence from the recent Group of 20 summit in Rome — Putin attended via video connection due to concerns about COVID-19 – and stated, "I hope we can meet in person the next time."

"It was a useful meeting," Sullivan said of the White House meeting, which allowed Biden to lay out the US's position candidly.

While the US and Russian presidents spoke, Ukraine grew increasingly concerned about the tens of thousands of Russian troops stationed along its border. Ukraine's leaders said that Russia had exacerbated the simmering problem by sending tanks and snipers into war-torn eastern Ukraine to "provoke retaliatory fire" and prepare the groundwork for a possible invasion.

According to an administration official speaking on the condition of anonymity to discuss a sensitive topic, US intelligence authorities have been unable to verify that assertion independently. However, the individual stated that the White House had addressed concerns directly with the Russians about "reverting to their old playbook" and provoking the Ukrainians.

According to the Kremlin's post-call summary, "Putin emphasized that it is incorrect to blame Russia for NATO's dangerous attempts to expand its presence on Ukrainian territory and military potential near Russian borders."

Additionally, according to the Kremlin, the Russian leader recommended lifting all mutual limits on diplomatic missions and assisting in the normalization of other elements of bilateral relations. According to Sullivan, the leaders have directed their staff to continue negotiations on that point.

The leader-to-leader talk — Biden speaking from the Situation Room of the White House, Putin from his villa in Sochi — was one of the most significant moments of Biden's presidency, occurring during a critical period. According to US intelligence authorities, Russia has massed 70,000 troops along the Ukraine border and is preparing for an attack early next year.

According to Sullivan, the US believes Putin has not decided to invade.

Biden served as vice president in 2014 when Russian troops marched into Ukraine's Crimean peninsula and claimed the area. According to aides, the Crimea incident — one of the darker moments on the international scene for then-US President Barack Obama — hangs big as Biden considers the present burning conflict.

Republicans in Washington present this moment as a critical test of Biden's global leadership. Biden campaigned on a platform of reestablishing American leadership following former US President Donald Trump's emphasis on an "America first" foreign policy. Republicans, on the other hand, argue that he has been ineffectual in slowing Iran's march toward nuclear weapons and has done far too little to oppose dictatorial leaders such as China's Xi Jinping and Russia's Putin.

"Beijing and Tehran's fellow authoritarians will be watching how the free world responds," Senate Minority Leader Mitch McConnell stated from the Senate floor before the Biden-Putin summit.

Sullivan stated that Biden and Putin had a "constructive discussion" about the Iran nuclear deal, describing it as an area where the two countries might collaborate.

"The more Iran demonstrates a lack of seriousness at the negotiating table," he added, the greater the sense of solidarity between the US and the 2015 nuclear deal's participants, which include Russia and the European Union.

Trump, who demonstrated extraordinary devotion to Putin during his presidency, stated in a statement that "Vladimir Putin looks at our pitiful surrender in Afghanistan, leaving behind dead Soldiers, American citizens, and $85 billion in military equipment." He then fixes his gaze on Biden, and he is unconcerned!"

Biden met with the United Kingdom, France, Germany, and Italy on Monday in advance of the Putin conversation to discuss messaging and potential sanctions. He also followed up with them after his call to inform them of the outcome. Biden is also scheduled to speak with Ukrainian President Volodymyr Zelenskyy.

According to commentators, Putin appears to view the current scenario as an opportunity to rebalance the power dynamic in the US-Russia relationship.

Apart from Ukraine, many other contentious subjects are on the agenda, including cyberattacks and human rights. Before the call, Kremlin spokesman Dmitry Peskov stated that overall, US-Russian ties are in "a rather dire state."

"Russia has never had the intention of attacking anyone," Peskov stated. He described the Biden-Putin phone talk as a "working conversation during a very trying period" in which "the escalation of tensions in Europe is unprecedented."