Top US and Russian diplomats will meet in Saudi Arabia on Tuesday for talks on resetting the countries' fractured relations and making a tentative start on trying to end the Ukraine war.
Both sides played down the chances that the first high-level meeting between the countries since Moscow invaded Ukraine in 2022 would result in a breakthrough.
Nevertheless, the very fact of the talks has triggered concern in Kyiv and Europe -- left reeling by Washington's dramatic diplomatic moves towards the Kremlin.
Ukrainian President Volodymyr Zelensky said Kyiv was not invited to the discussions in Riyadh, while European leaders were gathering in Paris for emergency talks on how to respond to the radical pivot by the new US administration.
Preparations for a possible summit between presidents Donald Trump and Vladimir Putin are also set to be on the agenda.
Trump is pushing for a swift resolution to the three-year conflict in Ukraine, while Moscow sees his outreach as a chance to gain concessions on some of its long-standing gripes about Washington's military presence in Europe.
Zelensky said Kyiv "did not know anything about" the talks in Riyadh, according to Ukrainian news agencies, and that it "cannot recognise any things or any agreements about us without us".
Moscow said ahead of the meeting that Putin and Trump wanted to move on from "abnormal relations" and that it saw no place for Europeans to be at any negotiating table.
Russia's Foreign Minister Sergei Lavrov and senior Putin aide Yuri Ushakov will meet with US Secretary of State Marco Rubio, National Security Advisor Mike Waltz and Special Envoy Steve Witkoff.
- Possible Trump-Putin summit -
Kremlin spokesman Dmitry Peskov told reporters the talks would be "primarily devoted to restoring the whole complex of Russian-American relations", alongside discussions on "possible negotiations on a Ukrainian resolution, and organising a meeting between the two presidents".
Moscow, which for years has sought to roll back NATO's presence in Europe, has made clear it wants to hold bilateral talks with the United States on a plethora of broad security issues, not just a possible Ukraine ceasefire.
Before invading in February 2022, Putin was demanding the military alliance pull its troops, equipment and bases out of several eastern members that were under Moscow's sphere of influence during the Cold War.
The prospects of any talks leading to an agreement to halt the Ukraine fighting are unclear.
Both Moscow and Washington have cast the meeting as the beginning of a potentially lengthy process.
"I don't think that people should view this as something that is about details or moving forward in some kind of a negotiation," US State Department spokesperson Tammy Bruce said.
Russia's Ushakov told state media the talks would discuss "how to start negotiations on Ukraine."
"The tasks are more or less clear to us," he added.
Both Kyiv and Moscow have ruled out territorial concessions and Putin last year demanded Ukraine withdraw its troops from even more territory.
Zelensky will travel to Turkey on Tuesday to discuss the conflict with President Recep Tayyip Erdogan, and then Saudi Arabia a day later.
He does not plan to hold talks with either the US or Russian delegations, his spokesman said Monday.
Zelensky said last week he was prepared to meet Putin, but only after Kyiv and its allies had a common position on ending the war.
As European leaders gathered in Paris for an emergency security summit, Russia's Lavrov said Monday he saw no point in them taking part in any Ukraine talks.
"I don't know what they would do at the negotiating table... if they are going to sit at the negotiating table with the aim of continuing war, then why invite them there?," he told a press conference in Moscow.
Germany on Monday said "direct contact between the Americans and the Russians is not a bad thing if it is about finding a way to a durable and lasting peace."
Moscow heads into the Saudi talks boosted by recent gains on the battlefield.
Its better resourced troops are pushing Ukraine back across the 1,000-kilometre (620-mile) front line.
Kyiv also faces the prospect of losing vital US military aid, long criticised by Trump.
Russia's army on Monday said its forces had captured a small settlement in northeastern Ukraine and also retaken control of a village in its western Kursk region, where Ukraine launched a shock counter-offensive last August.