LONDON– A ceasefire agreement has been reached between Israel and Hamas, Qatari officials announced on Wednesday. This interrupted more than 15 months of fierce fighting in Gaza, during which the Middle East, in the words of President Joe Biden, “fundamentally changed”.

As talks to end the Israel-Hamas conflict progressed slowly in Qatar last year, it appeared at times that an agreement was close, but each time one or both sides withdrew from the negotiating table before it could be finalized.

Disputes arose during the high-risk negotiations over the terms, which always included the return of the remaining hostages by Hamas and Israel’s military withdrawal from the Gaza Strip.

The deal also follows the high-profile assassinations last year of Hamas leaders Ismail Haniyeh and Yahya Sinwar – with Sinwar being a key architect of the October 7, 2023 terrorist attack on Israel – as well as Hezbollah leader Hassan Nasrallah. Israel has accepted responsibility for their deaths.

Throughout, the focus has been on the brutal war in Gaza, whose near-daily death toll has dwarfed efforts to stop it.

But on Wednesday, officials announced that Israel and Hamas had finally reached an agreement that negotiators hope will scale back and eventually end the war.

The agreement begins on Sunday. In the first, six-week phase, some Israeli forces will be withdrawn to allow more aid to flow in and 33 hostages in Gaza will be released, including women, children and the elderly, said the statement from Qatari Prime Minister Sheikh Mohammed bin Abdulrahman Al Thani. A number of Palestinian prisoners will also be released, he said.

According to the Hamas delegation in Doha, the terms to which Hamas agreed included the gradual complete withdrawal of Israeli troops from the Gaza Strip, including the Philadelphi Corridor, and the handover of 33 dead and alive Israeli prisoners in exchange for their release 1,000 Palestinian prisoners. According to the Hamas delegation, negotiations for the release of the remaining hostages were being completed gradually.

For more than a year, the two sides have been locked in a fierce and brutal conflict in Gaza, a bloody contest of attrition sparked by Hamas’ deadly surprise attack in southern Israel. According to Israeli authorities, more than 1,200 people were killed and another 253 were taken hostage.

More than 46,000 people have been killed and nearly 110,000 injured in the war between Israel and Hamas in Gaza, according to the Hamas-run Gaza Health Ministry. This number does not distinguish between civilians and combatants. However, according to the Ministry of Health, more than 14,000 children and 8,000 women were killed. The Israel Defense Forces (IDF) claimed to have killed more than 15,000 combatants over the course of the war.

After the start of the new year, the mood seemed to change fundamentally. On Monday, President Biden announced that mediators were “on the verge” of reaching an agreement.

The president and his top diplomats, including Secretary of State Antony Blinken, had pushed for a shutdown while in office. They said they wanted the deal to happen before Jan. 20, when President-elect Donald Trump takes office again.

Biden laid the groundwork for the deal in May 2024

A source told ABC News in February 2024 that Israeli officials had agreed to the terms of a deal that included the release of 40 hostages. Officials from Qatar, Egypt, Israel and the United States met in Paris to work out the details, which included the release of some Palestinians detained by Israel, the source said at the time.

But that attempt seemed to falter. In May, talks were again at a “critical” stage, White House spokesman John Kirby said at the time. It was said that Hamas would agree to a deal, but the next month the US said the militant group was unwilling to sign a deal.

The talks then stalled in July when Hamas leader Ismail Haniyeh, a key facilitator in the talks, was killed in Iran. The group’s militant leader, Yahya Sinwar, was killed in Gaza in October, bringing new uncertainty to the trial.

The talks in Doha were mediated throughout by the Qataris, including Emir Sheikh Tamim bin Hamad Al Thani, and the Egyptians with help from the US and others.

According to a report from the White House, Biden and the Qatari leader spoke on Sunday. Both “emphasized the urgent need for an agreement” to provide relief to the hostage families.

“We remain confident that with every step we get closer to returning everyone home,” the Hostage Families Forum said on Tuesday morning.

An agreement would also provide a much-needed “surge” in humanitarian aid to Gaza, Biden said.

The deal that was finally nearing was based on what Biden outlined in May 2024, an agreement that was unanimously approved at the time by the United Nations Security Council, the White House said.

“Today we have reached a point that is closest to an agreement on Gaza,” a Qatari foreign ministry spokesman said on Tuesday.

As the negotiations continued, sticking points became public

Previous humanitarian pauses have repeatedly raised hopes of a permanent ceasefire, but fighting has continued.

A brief ceasefire occurred in November 2023. During this ceasefire, more than 100 hostages taken during the October 7 attacks were released and, in return, 240 Palestinian prisoners and detainees were released.

Hamas accused Israel of refusing to extend the ceasefire, but Israel and the US said it was Hamas that ended the ceasefire by firing rockets into the Israeli town of Sderot.

Talks aimed at achieving a more lasting peace failed but were eventually resumed, despite Hamas’s repeated claims that Israeli Prime Minister Benjamin Netanyahu had torpedoed the negotiations to strengthen his domestic political position and legal pressure and opposition demands for new elections to ward off. The militant group also led repeated killings of Hamas leaders and Iranian and Hezbollah officials in Lebanon, Iran and Syria.

Netanyahu, meanwhile, said the continued deaths of hostages in Hamas captivity showed the group had no interest in peace. Publicly, the prime minister and most of his top officials remained committed to their goal of “wiping out” Hamas in its entirety.

The Biden administration’s frustration with its inability to bring the two sides to an agreement was often evident, especially as the death toll in Gaza and elsewhere continued to rise.

In September – shortly after Israel remotely detonated explosives hidden in Hezbollah pagers and walkie-talkies across Lebanon – Blinken said mediation efforts had been undermined “again and again.”

Each time the talks progressed, Blinken said, “We have experienced an event that makes the process more difficult and could derail it.”

A final push by two governments

Trump’s re-election victory in November gave fresh impetus to stalled negotiations, with Trump and his new Middle East envoy Steve Witkoff making clear the new president’s desire for an agreement before his Jan. 20 inauguration.

Trump threatened that “all hell will break loose in the Middle East” if the remaining Gaza hostages are not released by his return to office. “It won’t be good for Hamas and, frankly, it won’t be good for anyone,” he said.

Witkoff repeatedly traveled to the region to try to reach a deal, telling reporters that he and Biden envoy Brett McGurk had “collaborated” in their pursuit of a deal.

The Biden administration, Blinken said, is “very much” hoping to get the deal “over the finish line in the next two weeks, the time we have left.”

Negotiators returned to Doha in early January and senior officials – including Mossad chief David Barnea – later joined the talks as they neared a conclusion.

In the final days of talks, both Israeli and Hamas representatives signaled their willingness to reach an agreement, even as far-right elements of the Netanyahu government again threatened to collapse the ruling coalition in protest against a ceasefire.

ABC News’ Will Gretsky, Joe Simonetti and Shannon K. Kingston contributed to this report.