This week is being described as "critical" for peace talks between Ukraine and Russia.
US Secretary of State Marco Rubio says the White House can't keep trying to help if a deal isn't going to "come to fruition".
Following a one-to-one meeting with Volodymyr Zelenskyy in the Vatican at the weekend, Donald Trump said he doubts Vladimir Putin is willing to end the war.
Marco Rubio has told NBC News the US president has reasons to be optimistic - but he must also be realistic:
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