Donald Trump said Sunday that a deal to end Russia's invasion of Ukraine is closer than ever, though no breakthrough was reported on the contentious issue of territory following fresh talks with both countries' leaders.

Trump, who had promised a peace deal on day one of his nearly year-old presidency, said it would become clear within weeks whether it was possible to solve the conflict that has killed tens of thousands of people.

In a pre-New Year's diplomatic sprint, Trump brought to his Florida estate Ukrainian President Volodymyr Zelenskyy, who described a peace plan as 95% complete despite Russia unleashing major new attacks a day before on Kyiv's residential areas.

Much like when Zelenskyy last met Trump in October, Russian President Vladimir Putin also spoke shortly beforehand by telephone with the U.S. leader, who immediately insisted that Moscow was "serious" about peace despite the assault.

"I really believe we're, Mr. President, probably closer than – far closer than – ever before with both parties," Trump said with Zelenskyy at his side in the tea room of his Mar-a-Lago estate.