U.S. and Russian officials met on Tuesday in Riyadh for their first talks on ending the war in Ukraine, as Kyiv and its European allies watched anxiously from the sidelines and Moscow raised a new demand that NATO formally disavow a membership promise it made to Ukraine in 2008.

The talks in the Saudi capital underscored the rapid pace of U.S. efforts to halt the conflict, less than a month after President Donald Trump took office and six days after he spoke by phone to Russian President Vladimir Putin.

Ukraine and European leaders are worried that Trump could cut a hasty deal with Moscow that ignores their security interests, rewards Russia for invading its neighbour and leaves Putin free to threaten Ukraine or other countries in the future.

Critics say that Trump's team, by ruling out NATO membership for Ukraine and saying that Kyiv's desire to win back all its lost territory is an illusion, has made major concessions in advance. U.S. officials say they are simply recognising reality.

Ukraine says no peace deal can be made on its behalf. "We, as a sovereign country, simply will not be able to accept any agreements without us," President Volodymyr Zelenskiy said last week.

Hours after the start of the Riyadh meeting, Russian Foreign Ministry spokeswoman Maria Zakharova told reporters in Moscow it was "not enough" for NATO not to admit Ukraine as a member.

She said the alliance must go further by disavowing a promise it made at a summit in Bucharest in 2008 that Kyiv would join at a future, unspecified, date.

"Otherwise, this problem will continue to poison the atmosphere on the European continent," she said. There was no immediate response from NATO members or the United States.

In Riyadh, three U.S. officials in the first month of their jobs - Secretary of State Marco Rubio, national security adviser Mike Waltz and Trump's Middle East envoy Steve Witkoff - were lined up opposite two veterans of Russian diplomacy. Foreign Minister Sergei Lavrov has been in his role since 2004, and Kremlin aide Yuri Ushakov has served as Putin's foreign policy adviser since 2012.

Media were allowed to film the two delegations, seated on opposite sides of a polished wooden table with large white floral arrangements.

The officials ignored shouted questions from reporters asking whether the U.S. was sidelining the Ukrainians and what concessions Washington was demanding of Moscow.

The Kremlin said the Riyadh talks may bring clarity on a possible meeting between Trump and Putin, which both men have said they are keen to hold.