US President Donald Trump has said he thinks Ukraine would be willing to give up Crimea as part of a peace deal with Russia. Trump said he believed Volodymyr Zelensky was willing to cede control of the Eastern European peninsula which was illegally annexed by Russia in 2014 to ensure peace in the region. Responding to reporters who asked whether Zelensky was ready to "give up" the territory, the US leader replied: "Oh, I think so".

His Ukrainian counterpart has adamantly refused such proposals in the past, countering that Crimea belongs to Ukraine and that he doesn't have the authority to legally recognise Vladimir Putin's occupation. The comment comes hours after a historic meeting between the two leaders at Pope Francis's funeral on Saturday, when they engaged in one-on-one talks that the White House described as "very productive".

Trump also described the tête-à-tête as "a beautiful meeting" in "the nicest office I've ever seen" and praised the Ukrainian president for "doing a good job [and] working hard".

He said Crimea had been discussed "very briefly" and added that Zelensky had seemed "calmer", in an apparent reference to the public bust-up between the two presidents over the Eastern European conflict in February.

The weekend marked a shift in his tone towards Russia, suggesting on social media that Putin might "[not] want to stop the war" and could just be "tapping me along".

He doubled down on the new rhetoric while addressing journalists last night, calling on Russia to "stop shooting, sit down and sign a deal".

It comes after Sergei Lavrov, Russia's foreign minister, said Crimea is a "done deal" and that the country would "not negotiate its town territory", as the two countries enter what the US has called a "critical week" for peace talks.

The US's push to recognise Crimea as part of Russia in negotiations has met with criticism from Ukraine and its allies in Europe.

But fears remain that Trump could walk away from the table altogether if a ceasefire is not forthcoming. Secretary of State Marco Rubio said on Sunday that a deal was "close but ... not close enough".

"This week is going to be a really important weak in which we have to make a determination about whether this is an endeavour that we want to continue to be involved in, or if it's time to ... focus on some other issues that are equally, if not more, important," he said.