By John Irish

PARIS (Reuters) - The United States and its European allies are finalising a proposal for a 30-day ceasefire in Ukraine that if refused would see them jointly impose new sanctions on Russia, a French diplomatic source said on Friday.

U.S. President Donald Trump called on Thursday for a 30-day unconditional ceasefire between Russia and Ukraine, warning that Washington and its partners would impose further sanctions if the ceasefire was not respected.

Ukraine has expressed readiness to accept the U.S. proposal. Russia has unilaterally declared a three-day ceasefire running from May 8-10 to coincide with the 80th anniversary of the end of World War Two.

"We're not completely with a finalised project, but we hope that we're at a moment of convergence," said the diplomatic source, speaking on condition of anonymity.

"What could happen in the coming hours and days, there could be an announcement of a ceasefire either of 30 days or compartmentalized, which is still being discussed."

The source said there were still discussions on whether to announce a unilateral ceasefire or to give a short response time to Russia, although if it refused then new American and EU sanctions would be imposed on Moscow.

The two sides are coordinating on the sanctions packages.

French Foreign Minister Jean-Noel Barrot, who was in Washington last week to meet U.S. Secretary of State Marco Rubio, will join President Emmanuel Macron in Kyiv on Saturday, where there will be a hybrid meeting of Ukraine's closest allies and discussions on the U.S.-European proposal.

The source said political and technical talks between Europe and the U.S. had stepped up since last week. Trump and Macron spoke on Thursday to discuss the ceasefire proposal.

"We felt in the discussions with the Americans a certain irritation towards the Russian posture, the lack of reactivity and seriousness in its responses to what was proposed before," the source said. "The decision is practically taken."

(Reporting by John Irish; Editing by GV De Clercq and Alex Richardson)