US and Russian officials began talks in Saudi Arabia on Monday aimed at making progress towards a broad ceasefire in Ukraine.
The US is eyeing a separate Black Sea maritime ceasefire deal before securing a wider agreement.
The talks, which followed US negotiations with Ukraine in Saudi Arabia on Sunday, come as US President Donald Trump intensifies his drive to end the three-year-old conflict after he last week spoke to both Ukrainian President Volodymyr Zelenskyy and Russian President Vladimir Putin.
A source briefed on the planning for the talks said the US side was being led by Andrew Peek, a senior director at the White House National Security Council, and Michael Anton, a senior State Department official.
The White House says the aim of the talks is to reach a maritime ceasefire in the Black Sea, allowing the free flow of shipping, though the area has not been the location of intense military operations in recent months.
Russia will be represented by Grigory Karasin, a former diplomat who is now chair of the Russian upper house of parliament's Foreign Affairs Committee, and by Sergei Beseda, an adviser to the director of the Federal Security Service, the main successor agency to the Soviet-era KGB.
Trump, who has repeatedly called for an end to the war in Ukraine, has expressed broad satisfaction over the way talks have been going and has been complimentary about Putin's engagement in the process so far.
He said on Saturday that efforts to stop further escalation in the conflict were "somewhat under control".
But there is scepticism among major European powers over whether Putin is ready to make meaningful concessions or will stick to what they see as his maximalist demands that do not appear to have changed since he sent tens of thousands of troops into Ukraine in 2022.
Putin says he is ready to discuss peace but that Ukraine must officially drop its NATO ambitions and withdraw its troops from the entirety of the territory of four Ukrainian regions claimed and mostly controlled by Russia.
The push for a Black Sea ceasefire
White House national security adviser Mike Waltz told CBS' "Face the Nation" on Sunday that the US, Russian and Ukrainian delegations were assembled in the same facility in Riyadh.
Beyond a Black Sea ceasefire, he said, the teams will discuss "the line of control" between the two countries, which he described as "verification measures, peacekeeping, freezing the lines where they are."
He said "confidence-building measures" are being discussed, including the return of Ukrainian children taken by Russia.
The Kremlin said the talks will be "mainly to study the prospects for the possible implementation of a well-known initiative related to the safety of navigation in the Black Sea."
Turkey and the United Nations helped mediate the so-called Black Sea Grain Initiative, a deal struck in July 2022 that allowed the safe export of nearly 33 million metric tons of Ukrainian grain across the Black Sea despite the war.
Russia withdrew from the agreement in 2023, complaining that its own food and fertiliser exports faced serious obstacles, though Russia is not currently facing serious problems getting its grain to market by the Black Sea.
Ukraine's defence minister, Rustem Umerov, the head of the Ukrainian delegation, said on Facebook that the U.S.-Ukraine talks included proposals to protect energy facilities and critical infrastructure.
U.S. special envoy Steve Witkoff, who met Putin in Moscow in early March, played down concerns among Washington's NATO allies that Moscow could be emboldened by a deal and invade other neighbours.
"I just don't see that he wants to take all of Europe. This is a much different situation than it was in World War Two, Witkoff told Fox News.
"I feel that he wants peace," Witkoff said of Putin.
