JERUSALEM (Reuters) - Israel is preparing to receive the bodies of four hostages from Gaza on Thursday and is working on bringing back six living captives on Saturday, an Israeli security official said on Monday.

If the two handovers are successful, only four hostages, all presumed dead, would remain in Gaza of the 33 due to be released in the first phase of a ceasefire agreement reached last month to halt the war between Israel and the Palestinian militant group Hamas.

The ceasefire deal, reached with the help of Qatari and Egyptian mediators, has remained on track despite a series of temporary setbacks and accusations on both sides of violations to the agreement that have threatened to derail it.

Hamas has accused Israel of blocking the delivery of housing materials for the tens of thousands of Gazans forced to shelter from the winter weather among the ruins left by 15 months of Israeli bombardment.

Israel has denied the accusation but Zeev Elkin, a member of Prime Minister Benjamin Netanyahu's security cabinet, confirmed that a quantity of mobile homes was standing at the border.

He said Israel would use "any leverage" it had over Hamas to secure the return of the 33 hostages due to come out in the first phase of the deal, which includes the release of Israeli hostages in exchange for hundreds of Palestinian prisoners and detainees and the withdrawal of Israeli troops.

"Israel has a goal of bringing forward the release of the first phase hostages, certainly the living ones," he told public broadcaster Kan.

So far, 19 Israeli hostages have been returned, as well as five Thais, who were handed over in an unscheduled release. Hamas has said 25 of the 33 hostages due for release in the first phase are alive.

The ceasefire deal has been overshadowed by U.S. President Donald Trump's call for Palestinians to be moved out and for Gaza to be taken over as a waterfront development under U.S. control.

But officials say work has begun on the second phase of the deal, which would would address the return of the remaining hostages and the Israeli withdrawal.

An Israeli team has already travelled to Cairo and the security cabinet also cleared a high-level Israeli delegation to travel to Qatar for talks on the second phase.

"We all want to proceed to phase two and release the hostages, the question is under what conditions is the war ended," Elkin said. "This is the main issue for the negotiations of the second phase."

The hostages were taken in the Hamas-led cross-border attack on October 7, 2023, which also killed about 1,200 people in southern Israel, according to Israeli tallies.

Israel's retaliatory assault on Gaza has killed more than 48,000 Palestinians, according to Palestinian health officials, laid waste to much of the enclave, and displaced hundreds of thousands.

(Reporting by Maayan Lubell; writing by James Mackenzie; Editing by Hugh Lawson and Angus MacSwan)