JERUSALEM — Israel and Hamas began a 72-hour humanitarian cease-fire early Friday, with an agreement to negotiate for a more durable truce in the 24-day-old Gaza war.

In a statement released in New Delhi, where U.S. Secretary of State John Kerry is traveling, the U.S. and U.N. said they had gotten assurances that all parties to the conflict had agreed to an unconditional cease-fire.

“This humanitarian cease-fire will commence at 8 a.m. local time on Friday, Aug. 1, 2014. It will last for a period of 72 hours unless extended. During this time the forces on the ground will remain in place,” the statement said.

The statement said the cease-fire is critical to give civilians a much-needed reprieve from violence. During this period, civilians in Gaza will receive humanitarian relief and have time to bury the dead, take care of the injured and restock food supplies. The time also will be used to repair water and energy infrastructure.

Palestinian officials say 17 Palestinians, including 10 members of one family, were killed in Israeli strikes just before the cease-fire began.

Health official Ashraf al-Kidra said the family members were killed in an airstrike early Friday on their home in the southern town of Khan Younis. Gaza police reported heavy Israeli tank shelling in northern and eastern Gaza.

Earlier, the Israeli military said it was calling up an additional 16,000 reserve soldiers to pursue its campaign against the Islamic militants.

At least 1,441 Palestinians have been killed, three-quarters of them civilians, since hostilities began on July 8, according to Gaza health officials – surpassing the 1,410 Palestinians killed in 2009. Israel says 56 soldiers, two Israeli civilians and a Thai agricultural worker have died – also far more than the 13 Israeli deaths in the previous campaign.

In Geneva, the U.N. High Commissioner for Human Rights Navi Pillay accused both Israel and Hamas militants of violating the rules of war.

She said Hamas is violating international humanitarian law by “locating rockets within schools and hospitals, or even launching these rockets from densely populated areas.” But she added that this did not absolve Israel from disregarding the same law.

The Israeli government, she said, has defied international law by attacking civilian areas of Gaza such as schools, hospitals, homes and U.N. facilities. “None of this appears to me to be accidental,” Pillay said. “They appear to be defying – deliberate defiance of – obligations that international law imposes on Israel.”

Pillay also took aim at the U.S., Israel’s main ally, for providing financial support for Israel’s “Iron Dome” anti-rocket defense system. The Iron Dome system has been credited with saving countless lives as Hamas militants fired nearly 3,000 rockets at Israel.

At the United Nations, Israel’s Ambassador Ron Prosor responded to criticism of his country, saying: “I think the international community should be very vocal in standing with Israel fighting terrorism today because if not, you will see it on your doorstep tomorrow.”