Qatar will stop trying to mediate a Gaza ceasefire deal until Hamas and Israel show a "sincere willingness" to return to the negotiating table, an official briefed on the matter told Reuters on Saturday, in the biggest setback to efforts to reach a truce since the war began.

The Gulf country has also concluded that Hamas' political office in Doha "no longer serves its purpose", the official added, in a blow to the Palestinian militant group whose top leaders have been assassinated by Israel.

Qatar, alongside the United States and Egypt, has played a major role in rounds of so-far fruitless talks to broker a ceasefire to the year-long war in Gaza. The latest round of talks in mid-October failed to produce a deal, with Hamas rejecting a short-term ceasefire proposal.

"The Qataris have said since the start of the conflict that they can only mediate when both parties demonstrate a genuine interest in finding a resolution," the official said, adding that Qatar had notified Hamas, Israel and the U.S. administration of its decision.

Washington had told Qatar that Hamas' presence in Doha was no longer acceptable in the weeks since the Palestinian militant group rejected the latest proposal to achieve a ceasefire and a hostage deal, a U.S. official said on Friday.