Ukraine peace negotiations are entering a “critical week”, the US Secretary of State said after talks held on the sidelines of the Pope’s funeral.

Marco Rubio said “we’re close, but we’re not close enough” as he warned the US could still walk away if both sides do not make concessions.

He said the US has “options” to hold accountable those obstructing any agreement, and again threatened sanctions on Russia.

Mediators are urging Russia and Ukraine to enter direct talks to agree on a ceasefire based on a framework plan presented by the US that includes freezing the front lines and Ukraine giving up Crimea.

On Saturday, Donald Trump appeared to have lost patience with the Kremlin, saying that he was considering imposing sanctions and accusing Vladimir Putin of “tapping him along.”

Earlier in the day, he had met Volodymyr Zelensky at Pope Francis’ funeral in Rome. It was the first time the two leaders had met face-to-face since a disastrous meeting at the White House in late February.