The top US and Russian diplomats made no major breakthrough at talks on Ukraine today but agreed to keep talking to try to resolve a crisis that has stoked fears of a military conflict.
After the talks in Geneva, US Secretary of State Antony Blinken warned of a "swift, severe" response if Russia invades Ukraine after massing troops near its border.
Russian Foreign Minister Sergei Lavrov said Moscow was still waiting for a written response to its demands for security guarantees.
But both said they were open to further dialogue, and Mr Blinken saw grounds to hope that mutual security concerns could be addressed.
"Based on the conversations we've had - the extensive conversations - over the past week and today here in Geneva I think there are grounds for and a means to address some of the mutual concerns that we have about security," Mr Blinken said.
He described the talks as "frank and substantive" and said Russia now faced a choice.
"It can choose the path of diplomacy that can lead to peace and security, or the path that will lead only to conflict, severe consequences and international condemnation," Mr Blinken told reporters, adding that diplomacy would be preferable.
"We've been clear - if any Russian military forces move across Ukraine's border, that's a renewed invasion. It will be met with swift, severe and a united response from the United States and our partners and allies."
Mr Lavrov said the ball was in Washington's court.
Describing the meeting as open and useful, he said Moscow would understand whether talks were on the right track once it had received a written response to its sweeping security demands from the US.
Russia's demands include a halt to NATO's eastward expansion and a pledge that Ukraine will never be allowed to join the Western military alliance.
"I can't tell you if we're on the right track or the wrong track. We'll understand this when we receive the American response on paper to all the points in our proposal," Mr Lavrov said.
Tatiana Stanovaya, head of political analysis firm R Politik, commented on Telegram: "This is partly a trap, of course, because any such written response will be used to discredit the US negotiating position."
Mr Blinken said he expected to share with Russia "our concerns and ideas in more detail and in writing next week" and said he and Mr Lavrov had "agreed to further discussions after that".
Russia and the US could hold another meeting next month to discuss Moscow's demands for security guarantees,
Mr Lavrov said Russia had worries of its own, "not about invented threats, but real facts that no one hides - pumping Ukraine with weapons, sending hundreds of western military instructors".
Asked about the possibility of a summit between President Vladimir Putin and US President Joe Biden, Mr Lavrov was circumspect.
'President Putin is always ready for contacts with President Biden'
"Let's not get ahead of ourselves, President Putin is always ready for contacts with President Biden, it's clear these contacts need to be seriously prepared," Mr Lavrov said.
Mr Blinken said of another potential meeting between Mr Biden and Mr Putin: "If we conclude, and the Russians conclude, that the best way to resolve things is through a further conversation between them, we're certainly prepared to do that."
The two presidents met in Geneva in June last year.
Washington's hopes of building a united front of opposition to Moscow were complicated by Mr Biden's comments at a news conference on Wednesday in which he suggested that allies might be divided on how to respond to a "minor incursion" by Russia in to Ukraine.
Mr Biden and his administration sought to row back on that yesterday, with the president saying that "if any, any assembled Russian units move across the Ukrainian border that is an invasion".
Before today's meeting, Mr Blinken swung through Europe to try to shore up US allies' commitments to hit Russia with economic sanctions if it goes ahead with an invasion of Ukraine.
In Kyiv on Wednesday, Mr Blinken assured Ukraine of US support.
Mr Blinken, before meeting German, French and British officials in Berlin yesterday, said Mr Putin could order an invasion imminently.
Mr Blinken spoke with Ukrainian Foreign Minister Dmytro Kulebaover the phone today and briefed him on his meetings with European and Russian officials, the State Department said in a statement, reaffirming Washington's support for Kyiv.
Mr Blinken's deputy, Wendy Sherman, and Mr Lavrov's deputy, Sergei Ryabkov, also met in Geneva last week, without a breakthrough.
Pentagon spokesman John Kirby said the military was looking at a range of options that might be needed in case allies in Europe ask for reassurance and support.
Some of those US military capabilities could come from within Europe or even from the US if needed, Mr Kirby said.
"Our job is to make sure that we're ready in case our allies need us," he added.