Trump's surprise offer to join the talks on Thursday in Istanbul came a day after Ukrainian President Volodymyr Zelenskiy, in a fresh twist to the stop-start peace talks process, said he would travel Turkey and wait to meet President Vladimir Putin there.
After Trump's announcement on Monday, US Secretary of State Marco Rubio discussed the "way forward for a ceasefire" in Ukraine with European counterparts, including the foreign ministers of Britain and France, and the EU's foreign policy chief, the State Department said on Monday.
Ukraine's Foreign Minister Andrii Sybiha and his German and Polish counterparts were also on the call, according to the readout.
Russian Foreign Minister Sergei Lavrov held talks late on Monday with his Turkish counterpart Hakan Fidan to discuss Moscow's direct talks with Kyiv - a proposal that came from Putin at the weekend, the Russian foreign ministry said.
It remained unclear who would travel from Moscow to Istanbul to take part in the direct talks, which would be the first between the two sides since the early days of the war that Russia launched with its invasion on Ukraine in February 2022.
There has been no response from the Kremlin to Zelenskiy's offer to meet Putin in Istanbul and Moscow was yet to comment on Trump's offer to join the talks.
If Zelenskiy and Putin, who make no secret of their contempt for each other, were to meet on Thursday it would be their first face-to-face meeting since December 2019.
"Don't underestimate Thursday in Turkey," Trump told reporters at the White House on Monday.
Trump's current schedule has him visiting Saudi Arabia, the United Arab Emirates and Qatar this week.
Ukraine and its European allies have been seeking to put pressure on Moscow to accept an unconditional 30-day ceasefire from Monday, with the leaders of four major European powers travelling to Kyiv on Saturday to show unity with Zelenskiy.
Earlier on Monday, the German government said Europe would start preparing new sanctions against Russia unless the Kremlin by the end of the day started abiding by the ceasefire.
Ukraine's military said on Monday that fighting along parts of the frontline in the country's east was at the same intensity it would be if there were no ceasefire.
Putin called the Western European and Ukrainian demands for a ceasefire "ultimatums" that the Kremlin said on Monday are for Russia an unacceptable language.
Konstantin Kosachev, chairman of the international affairs committee of the Federation Council, the upper house of Russia's parliament, told the Izvestia media outlet in remarks published on Tuesday that the talks between Moscow and Kyiv can move further than they did in the 2022.
"If the Ukrainian delegation shows up at these talks with a mandate to abandon any ultimatums and look for common ground, I am sure that we could move forward even further than we did," Izvestia cited Kosachev as saying.
