US and Russian officials held more than four hours of talks in Riyadh on Tuesday, their first on ending the war in Ukraine, as Kyiv and its European allies watched anxiously from the sidelines and Moscow raised a major new demand.

Interfax news agency quoted Russian negotiator Yuri Ushakov as saying the talks went well, and conditions were discussed for a meeting between presidents Donald Trump and Vladimir Putin.

Ushakov said a summit was unlikely to take place next week. But the talks in the Saudi capital underscored the rapid pace of US efforts to halt the conflict, less than a month after Trump took office and six days after he spoke by phone to Putin.

Even while the meeting was underway, Russia signalled a hardening of its demands.

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.

Ukrainian President Volodymyr Zelenskiy has consistently demanded NATO membership as the only way to guarantee Kyiv’s sovereignty and independence from its nuclear-armed neighbour.

He and European leaders are worried that Trump could cut a hasty deal with Moscow that ignores their security interests, rewards Russia for its invasion 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. US officials say they are simply recognising reality.