Joe Biden and Vladimir Putin held a virtual summit on Tuesday but made little apparent headway in defusing the crisis over Ukraine in the wake of a Russian troop buildup, and instead delegated officials from both countries to stay in contact.
The two leaders talked by videoconference for just over two hours, during which they laid out their positions.
"The discussion between President Biden and President Putin was direct and straightforward. There was a lot of give and take, there was no finger-wagging. But the president was crystal clear about where the United States stands on all of these issues," the US national security adviser, Jake Sullivan, said.
The Kremlin said Putin and Biden had traded threats regarding Russia's buildup of forces near the Ukrainian border. Putin accused Nato forces of undertaking "dangerous attempts to develop Ukrainian territory and increase its potential along our borders".
Putin went on to demand "reliable, legal guarantees" that would specifically prevent Nato from expanding its territory toward Russia or place missile systems in countries bordering Russia.
The US has repeatedly said it is Ukraine's right to decide its own security arrangements, but Sullivan said that Biden made clear that broader strategic talks between the Nato allies and Russia were possible if the threat of invasion receded.
Sullivan laid out some of the counter-measures the US and its allies would take in the event of an invasion, including reinforcements to Nato's eastern flank.
US allies in eastern Europe, he said, "will be seeking we expect additional capabilities and potentially additional deployments in the United States. We'll be looking to respond positively to those things in the event that there is a further incursion into Ukraine."
According to the Reuters news agency, US officials told members of congress on Tuesday they had an agreement with Germany to shut down the Nord Stream 2 gas pipeline linking Russia and northern Europe, if Moscow launched an offensive in Ukraine.
Sullivan did not go into detail on other economic measures, but among the other sanctions believed to be under consideration are a ban on the secondary market in Russian bonds, sanctions on large Russian corporations and banks and expulsion from the international electronic payments system Swift.
After the call, Biden spoke to the leaders of the UK, Germany, France and Italy by conference call. The president had consulted them on Monday, and the White House said they had agreed "to stay in close touch on a coordinated and comprehensive approach in response to Russia's military buildup on Ukraine's borders".
The Kremlin claimed that the two leaders had "agreed to instruct their representatives to engage in substantive consultations on these sensitive issues". That would indicate further talks at a lower level, continuing negotiations between the two countries despite the lack of any clear breakthrough in the talks.
Sullivan said that if the crisis could be defused, there was a diplomatic path open towards a rejuvenated Nato-Russia dialogue.
"The United States and our European allies would engage in a discussion that covers larger strategic issues, including our strategic concerns with Russia and Russia's strategic concerns," he said.
Before the talks, Putin greeted Biden informally, leaning back in his chair and waving at a television screen: "Hello, Mr President." Russian television reported that the talks were held one-on-one without any aides other than interpreters.
Russian officials said that Putin would press Biden in order to force Kyiv to abide by the 2015 Minsk agreements, an agreement that both Russia and Ukraine have accused the other side of violating. "It looks like Kyiv won't listen to anyone but the United States," the Russian foreign minister, Sergey Lavrov, said ahead of the talks on Tuesday.
The agreement stipulates that Ukraine reform its constitution and open direct talks with Russian-backed separatists, both of which are extremely unpopular in Kyiv. Analysts called the requests non-starters.
Russia also said that Putin would press Biden on his "red lines", including Kremlin opposition to both Ukraine's entry into Nato or considerable cooperation between Kyiv and the military alliance.
"Russia isn't going to attack anyone, but we have our own concerns and our own red lines. [Putin] has made them clear," Kremlin spokesman Dmitry Peskov told reporters before the talks.
Analysts said that Putin was prepared to use force in order to achieve his aims in Ukraine but that an offensive was not a foregone conclusion.
"Putin keeps raising the stakes quite intentionally in order to test the resilience of the west," said Pavlo Klimkin, the former Ukrainian foreign minister, who in an interview before the talks, predicted they would produce only modest results.
Klimkin said it was unlikely that Putin would order a quick drawdown of Russia's forces massed at the borders.
"They will stay," he said. "For the Russians it is important to start a discussion with the Americans and Europe on anything. On strategic stability on other issues. But also on so-called legal guarantees for Nato not to be further enlarged. This factor is very important with any dialogue with the United States. The forces will be put back [to base] only if he understands clearly that he lost or that he won. Otherwise not."
The US embassy in Kyiv denied reports on Tuesday evening that it was planning to evacuate government personnel or citizens from the country. "We are conducting normal contingency planning, as we always do, in the event the security situation severely deteriorates," the embassy said in a statement.