The question of eventual security guarantees for Ukraine has been front and centre during the latest US-led diplomatic push to broker a peace deal to end the conflict, now in its fourth year.

"Robust security guarantees will be essential and this is what we are now working to define," Mark Rutte said during a visit to Kyiv, speaking alongside Ukrainian President Volodymyr Zelensky.

US President Donald Trump, who hosted a meeting of European leaders with Rutte and Zelensky on Monday, said Russia had agreed to some Western security guarantees for Kyiv.

But Moscow later cast doubt on any such arrangement. Foreign Minister Sergei Lavrov said on Wednesday that discussing security guarantees without Russia was "a utopia, a road to nowhere".

On a visit to Kyiv, during which an air raid alert sounded across the city, Rutte said security guarantees were needed to ensure "Russia will uphold any deal and will never ever again attempt to take one square kilometre of Ukraine".

Zelensky said "the guarantees consist of what partners can give Ukraine, as well as what the army in Ukraine should be like" once the war ends.

"And it is too early to say who can provide military personnel, who can provide intelligence, who has a presence at sea or in the air, and who is ready to provide funding," he added.

Rutte also said it was "too early to exactly say what will be the outcome. But clearly, the US will be involved", adding: "We do not want a repeat of the Budapest Memorandum or the Minsk Agreement."

Moscow signed the Budapest Memorandum in 1994, which was aimed at ensuring security for Ukraine, Belarus and Kazakhstan in exchange for them giving up numerous nuclear weapons left from the Soviet era.

Russia violated that first by taking Crimea in 2014, and then by starting a full-scale offensive in 2022, which has killed tens of thousands of people and forced millions to flee their homes.