The encounter at the Dolmabahce Palace on the Bosphorus is a sign of diplomatic progress between the warring sides, who had not met face-to-face since March 2022.
Several vehicles arrived on Friday at the venue of talks in Istanbul involving delegations from Russia, Ukraine, the United States and Turkey, Reuters witnesses said.
Among them were an armoured vehicle, an ambulance, two white minibuses and several black cars.
But expectations for a major breakthrough, already low, were dented further on Thursday when Trump said there would be no movement without a meeting between himself and Russia's President Vladimir Putin.
Turkish Foreign Ministry sources said a meeting between Turkish, US and Ukrainian officials would take place late on Friday morning followed by talks between Turkish, Russian and Ukrainian delegations about midday.
Putin on Sunday proposed direct talks with Ukraine in Turkey, but has spurned a challenge from Ukrainian President Volodymyr Zelenskiy to meet him in person, and instead has sent a team of mid-ranking officials to the talks.
Zelenskiy said Putin's decision not to attend but to send what he called a "decorative" line-up showed the Russian leader was not serious about ending the war.Â
Russia accused Ukraine of trying "to put on a show" around the talks.
Russia says it sees them as a continuation of the negotiations that took place in the early weeks of the war in 2022, also in Istanbul.
But the terms under discussion then, when Ukraine was still reeling from Russia's initial invasion, would be deeply disadvantageous to Kyiv. They included a demand by Moscow for large cuts to the size of Ukraine's military.
With Russian forces now in control of close to a fifth of Ukraine, Putin has held fast to his longstanding demands for Kyiv to cede territory, abandon its NATO membership ambitions and become a neutral country.
Ukraine rejects these terms as tantamount to capitulation, and is seeking guarantees of its future security from world powers, especially the United States.
The US State Department's director of policy planning Michael Anton will represent the US in the talks, said a state department spokesperson.
The Russian delegation is headed by Kremlin aide Vladimir Medinsky and includes a deputy defence minister, a deputy foreign minister and the head of military intelligence.
Zelenskiy said on Thursday his team would be led by Defence Minister Rustem Umerov and include the deputy heads of Ukraine's its intelligence services, the deputy chief of the military's general staff and the deputy foreign minister.
