Israel and Hamas agreed to a deal to halt fighting in Gaza and exchange Israeli hostages for Palestinian prisoners, an official briefed on the deal told Reuters on Wednesday, opening the way to a possible end to a 15-month war that has upended the Middle East.

The agreement follows months of on-off negotiations brokered by Egyptian and Qatari mediators, with the backing of the United States, and came just ahead of the Jan. 20 inauguration of U.S. President-elect Donald Trump.

Israeli troops invaded Gaza after Hamas-led gunmen broke through security barriers and burst into Israeli communities on Oct. 7, 2023, killing 1,200 soldiers and civilians and abducting more than 250 foreign and Israeli hostages.

Israel's campaign in Gaza has killed more than 46,000 people, according to Gaza health ministry figures, and left the narrow coastal enclave a wasteland of rubble, with hundreds of thousands surviving the winter cold in tents and makeshift shelters.

As his inauguration approached, Trump repeated his demand that a deal be done swiftly, warning repeatedly that there would be "hell to pay" if the hostages were not released. His Middle East envoy Steve Witkoff worked with President Joe Biden's team to push the deal over the line.

Here are the main elements of the ceasefire deal, according to the official briefed on the agreement:

* A six-week initial ceasefire phase includes the gradual withdrawal of Israeli forces from central Gaza and the return of displaced Palestinians to northern Gaza

* The deal requires 600 truckloads of humanitarian aid to be allowed into Gaza every day of the ceasefire, 50 of them carrying fuel, with 300 of the trucks allocated to north

* Hamas will release 33 Israeli hostages, including all women (soldiers and civilians), children, and men over 50. Hamas will release female hostages and under 19s first, followed by men over 50

* Israel will release 30 Palestinian detainees for every civilian hostage and 50 Palestinian detainees for every Israeli female soldier Hamas releases

* Israel will release all Palestinian women and children under 19 detained since Oct. 7, 2023 by end of the first phase. The total number of Palestinians released will depend on hostages released, and could be between 990 and 1,650 Palestinian detainees including men, women and children

* Hamas will release the hostages over a six-week period, with at least three hostages released each week and the remainder of the 33 before the end of the period. All living hostages will be released first, followed by remains of dead hostages

* The implementation of the agreement will be guaranteed by Qatar, Egypt and the United States.

* Negotiations over a second phase of the agreement will begin by the 16th day of phase one and is expected to include the release of all remaining hostages, including Israeli male soldiers, a permanent ceasefire and the complete withdrawal of Israeli soldiers

* A third phase is expected to include the return of all remaining dead bodies and the start of Gaza's reconstruction, supervised by Egypt, Qatar and the United Nations.