Putin on Sunday proposed direct negotiations with Ukraine in Istanbul on Thursday "without any preconditions". But he did not say who would be attending from Moscow's side and his spokesman was unable to give further details on the matter on Wednesday.
Trump earlier this week urged Ukraine to attend the talks and Ukrainian President Volodymyr Zelenskiy quickly said he would be there, but only if Putin showed up, setting up a diplomatic standoff as part of an apparent contest to show Trump who wants peace more.
Trump on Wednesday said he himself was still considering whether to attend the talks in Turkey but did not know whether Putin would go, something that Zelenskiy has challenged the Kremlin leader to do "if he's not afraid".
"(Putin) would like me to be there, and that's a possibility ... I don't know that he would be there if I'm not there. We're going to find out," Trump told reporters aboard Air Force One en route to Qatar.
Trump wants the two sides to sign up to a 30-day ceasefire in what is Europe's biggest land war since World War II, and a Russian lawmaker on Wednesday said there could also be discussions about a huge prisoner of war exchange.
Zelenskiy backs an immediate 30-day ceasefire, but Putin has said he first wants to start talks at which the details of such a ceasefire could be discussed.
Trump, who is growing increasingly frustrated with both Russia and Ukraine as he tries to push them towards a peace settlement, said he was "always considering" secondary sanctions against Moscow if he thought it was blocking the process.
US officials have spoken about possible financial sanctions as well as potential secondary sanctions on buyers of Russian oil.
A Ukrainian diplomatic source told Reuters on Wednesday that Ukraine's leadership would decide on its next steps for peace talks in Turkey once there was clarity on Putin's participation.
"Everything will depend on whether Putin is scared of coming to Istanbul or not. Based on his response, the Ukrainian leadership will decide on the next steps," the source said.
If Putin agrees to join, it would be the first meeting between the leaders of the two warring countries since December 2019. Direct talks between negotiators from Ukraine and Russia last took place in Istanbul in March 2022, a month after Putin sent tens of thousands of troops into Ukraine.
Some unconfirmed Russian and US media reports had said that Russian Foreign Minister Sergei Lavrov and Yuri Ushakov, Putin's foreign policy aide, would be in Istanbul and ready to meet their Ukrainian counterparts.
But Russia's Kommersant newspaper, which is regarded as having good sources in the Russian Foreign Ministry and the Kremlin, said on Wednesday evening that Lavrov would not attend.
Asked earlier by reporters during a daily briefing if the Kremlin could reveal the make-up of the Russian delegation, spokesman Dmitry Peskov said: "We will do that when we get an instruction to do so from the president."
"The Russian delegation will be waiting for the Ukrainian delegation in Istanbul on May 15."
Trump has said he will send Secretary of State Marco Rubio and senior envoys Steve Witkoff and Keith Kellogg to Turkey, while also offering to attend himself.Â
