US President Donald Trump was set to speak with Russian leader Vladimir Putin, part of a renewed push by the White House to cement a cease-fire for the Ukraine war.

Trump was also scheduled to hold a separate phone call on May 19 with Ukrainian President Volodymyr Zelenskyy.

Steve Witkoff, a White House envoy who has met three times already with Putin, predicted the conversation with Putin would "will go a long way toward identifying where we are and how we complete this negotiation."

"They know each other. The president is determined to get something done here.... If he can't do it, then nobody can,"he said in an interview with ABC Newsover the weekend.

Trump had announced the calls after Russian and Ukrainian negotiations met in Istanbul for face-to-face talks. It was the first time the two sides have met since the early weeks after Russia launched its all-out invasion in February 2022.

"The subjects of the call will be stopping the 'bloodbath',"Trump wrote in a post to social media."Hopefully it will be a productive day, a cease-fire will take place, and this very violent war, a war that should have never happened, will end."

The Istanbul meetings, which included separate conversations with US officials, yielded only modest results, including an agreement to swap as many as 1,000 prisoners of war. There no pledge to halt fighting and over the weekend, Russia launched what Ukraine said was one of its largest drone barrages

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Russian negotiators reportedly made maximalist demands of Ukraine -- calling on Ukraine to withdraw its forces from regions partially occupied by Russia -- and other conditions that had been made in spring 2022. Those conditions have been widely rejected by Ukraine, and many of its Western allies, as nonstarters.

Since taking office in January, Trump had made resolving Russia's war on Ukraine a top foreign policy priority. Those efforts have been frustrated by Russia's continued offensive operations on the battlefield, and Moscow's unwillingness to agree to a 30-day cease-fire -- something Kyiv has signed on to.

After a period of initial tensions with Kyiv, White House frustrations have shifted to Moscow, and the tone of public remarks from US officials has sharpened. Trump has suggested Putin was "tapping" him along and seeking further talks without any genuine intention of seeking peace.

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"Are they tapping us along? Well, that's what we're trying to find out," Secretary of State Marco Rubio saidin an interview with CBS News broadcast May 18.

"On the one hand, we're trying to achieve peace and end a very bloody, costly, and destructive war, so there's some element of patience that is required," Rubio said. "On the other hand, we don't have time to waste."

Zelenskyy traveled to Turkey last week, along with his negotiators, and pledged to meet with Putin; the last time the two met was in 2019, before the war. But Putin announced at the last minute that he would not travel to Turkey.

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Zelenskyy also traveled to the Vatican over the weekend,seeking support from newly installed Pope Leo XIV. The Ukrainian leader also met with US Vice President JD Vance and Rubio in Rome.

It was Zelenskyy's first meeting with Vance since an acrimonious encounter in the White House in February, where Vance berated the Ukrainian leader before TV cameras.