Jim Michaels

USA TODAY

WASHINGTON — After more than three weeks of fighting and a mounting death toll in Gaza, Israel and Hamas agreed to a 72-hour unconditional cease-fire that took effect Friday morning, the United States and United Nations announced.

This is the longest cease-fire agreed to since the fighting began July 8. Whether it will last is uncertain. Previous cease-fires have been for shorter periods and marked by violations.

The humanitarian cease-fire will give "innocent civilians a much-needed reprieve from violence," Secretary of State John Kerry and U.N. Secretary-General Ban Ki Moon said in a joint statement.

Kerry acknowledged "there are no guarantees" that the lull would lead to a lasting peace in the region. "This is a difficult, complicated issue," he added.

Soon after the Israeli prime minister's office confirmed that Israel agreed to the truce, Hamas spokesman Sami Abu Zuhri said the Islamic militant group also had signed on, "as long as the other party is in agreement to it."

The joint statement said that Israeli and Palestinian delegations will be traveling to Cairo, where Egypt will try to broker a more "durable" agreement.

"During this period, civilians in Gaza will receive urgently needed humanitarian relief and the opportunity to carry out vital functions, including burying the dead, taking care of the injured and restocking food supplies," the statement said.

The Palestinian Health Ministry said Thursday that more than 1,400 Palestinians in Gaza have been killed since the conflict began, three-fourths of them civilians. Israel said 56 soldiers and three civilians have died.

Egypt has tried to negotiate a cease-fire previously but failed to get an agreement acceptable to both sides. Israel wants an end to rocket attacks and incursions through tunnels by the militant group, and Hamas wants a blockade of the Gaza Strip by Israel and Egypt lifted.

Israel initially launched aerial strikes in response to Hamas rocket attacks that have now exceeded 2,500, according to the Israel Defense Forces (IDF). It began a ground offensive into Gaza on July 17 to destroy the rockets and launchers and numerous tunnels Hamas has used to infiltrate Israeli territory.

Earlier this week Israel said it believed almost 5,000 rockets, about half the arsenal Hamas began with, remained in Hamas' hands.

The Israeli military's expanded ground offensive has destroyed much of Gaza, as civilian deaths and injuries, including many children, have climbed steadily. Schools, mosques, homes, marketplaces and the only power plant have been targeted, creating what the U.N. has called a growing humanitarian crisis.

On Thursday, Gaza health official Ashraf al-Kidra said at least 15 people were wounded, three critically, when a blast struck a mosque in the northern town of Beit Lahiya.

Gazans are facing power, water and food shortages, as well as the loss of homes and businesses and the death of relatives.

"I feel bad that I stopped selling desalinated water to people using my truck," said Gehad Sukker, 45, a Gaza resident and father of three. "But it's dangerous."

Ban said the Israeli shelling of a U.N. school that served as a shelter and caused multiple civilian deaths was "outrageous" and "unjustifiable." In Geneva, U.N. High Commissioner for Human Rights Navi Pillay accused both sides of committing war crimes. Pillay also criticized the U.S. for its financial assistance with Israel's Iron Dome defense system while providing no such defensive aid to Gazans.

The United States, which condemned Israel for shelling the school and Hamas for hiding weaponry in schools, confirmed it had resupplied Israel with undisclosed munitions from a U.S. stockpile in Israel. Rear Adm. John Kirby, the Pentagon press secretary, did not detail the weaponry. CNN, citing an anonymous U.S. defense official, said the ammunition included tank rounds and illumination rounds.

Israel said it has tried to minimize casualties by warning people to leave targeted areas before bombing them. It also has accused Hamas of hiding rockets in schools and mosques, and using civilians as "human shields."

Before the cease-fire was announced, Israel's ground forces were attempting to destroy 32 tunnels that Hamas had used to hide weapons and infiltrate fighters into Israel. Israel said it was no more than a few days away from destroying the remaining cross-border tunnels it has uncovered.

Prime Minister Benjamin Netanyahu previously has said he wouldn't accept any truce that will block Israel's goal of destroying the tunnel network. Hamas has said it will only lay down arms once Israel and Egypt give guarantees that a seven-year Gaza border blockade will be lifted.

Israel had called up 16,000 more reservists Thursday, a move that could have signaled an intention to widen the offensive. Israel has activated 86,000 reserves since the conflict began.

Prior to the cease-fire announcement, Hamas rocket fire continued to reach major Israeli cities, with one hitting a residential building in Kiryat Gat on Thursday. While Israelis said they, too, want the conflict to end, they are not optimistic.

"We all know that it is a game of politics," said Gary Sagiv, 49, from Kibbutz Elon in northern Israel. "We are sick and tired of the killings (on both sides) and want this to end. (But that) means no more rockets, no more kidnapping and no more tunnels."

Contributing: David Jackson in Washington, Yousef Al-Helou in Gaza City, Ilana Conway in Tel Aviv, the Associated Press