JERUSALEM — Hundreds of Palestinian prisoners in Israeli jails ended a hunger strike on Monday that had lasted for weeks, signing an agreement with the Israeli authorities that promised improved conditions, according to officials. The end of the strike calmed fears of widespread unrest in the event of a prisoner’s death.

“There is an agreement — the strike is over,” Sivan Weizman, a spokeswoman for the Israel Prison Service, said by telephone on Monday evening.

Qadura Fares, the president of the Palestinian Prisoners Society, based in Ramallah in the West Bank, said that the agreement was reached by prison leaders on behalf of all the Palestinian factions.

Israel said that Egypt and Jordan had played roles in helping to end the strike.

Among other provisions, the Israeli authorities said, the agreement calls for prisoners now in solitary confinement to be returned to the general prison population and for family visits to resume for prisoners from Gaza, which is under the control of Hamas, the more radical of the major Palestinian factions.

Israeli officials said they had made no commitment to end the practice of incarceration without formal charges or a trial, known as administrative detention, and that current administrative detainees would serve out their terms.

But Issa Qaraqe, the minister of prisoner affairs for the Palestinian Authority, which controls the West Bank, said earlier on Monday that there were understandings that the terms of the roughly 300 prisoners being held without charges would not be extended.

Most of the 4,500 Palestinian prisoners in Israeli jails have been tried and convicted of security offenses.

Israel’s internal security agency, known as the Shin Bet, said in a statement that the agreement became possible after the prisoners made a commitment “to completely halt terrorist activity inside Israeli prisons,” and “to refrain from all activity that constitutes practical support for terrorism, including recruiting people for terrorist activity, guidance, financing, coordinating among recruits, aiding recruits,” and related activities.

The two sides had seemed intent on reaching a deal before Tuesday, when the Palestinians commemorate the “nakba,” or catastrophe, on the anniversary of Israel’s declaration of independence in 1948. The war that followed the declaration led to the flight or expulsion of hundreds of thousands of Palestinians, and the day is traditionally observed with protest marches.

Mahmoud Abbas, the president of the Palestinian Authority, said over the weekend that the death of a hunger striker could be “disastrous” and that it could lead to the collapse of the security system in the West Bank.

Representatives of Mr. Abbas’s mainstream Fatah Party and of Hamas, the rival Islamic group, have been in Cairo in recent days for talks with Egyptian officials. Outside mediation was necessary because many of the striking prisoners were associated with groups with which Israel has no direct contact, including Hamas, which does not recognize Israel, and the even more militant Islamic Jihad. Complicating matters further, direct peace negotiations between Israel and the Fatah-dominated West Bank leadership have been suspended for more than 18 months.

Although only a minority of the hunger strikers were identified with Mr. Abbas’s secularist Fatah Party, he had taken the lead in pressing for a resolution. Israeli officials preferred to give Mr. Abbas the credit, and presented the agreement as a good-will gesture.

“In response to the request of the Palestinian president, Mahmoud Abbas, Israel has negotiated the end of the strike,” said Mark Regev, an Israeli government spokesman. “It is our hope that this decision will serve to build confidence between the parties and further peace.”

The two hunger strikers who have fasted the longest, Bilal Diab, 27, and Thaer Halahleh, 33, are both accused of working with Islamic Jihad in the West Bank. The group was the main force behind the firing of rockets into Israel from Gaza in recent months.

Khader Habib, an Islamic Jihad leader in Gaza, said that representatives were on their way to see Mr. Diab and Mr. Halahleh and explain the details of the agreement. Other prisoners told relatives that they were still on strike, awaiting instructions from prison leaders.

Mr. Diab and Mr. Halahleh have been without food for 76 days to protest their incarceration without formal charges. More than 1,600 prisoners had joined the strike since mid-April, posing an acute problem for Israel.

Most prisoners demanded improved conditions and the restoration of rights that were suspended while an Israeli soldier was held captive in Gaza. That soldier, Gilad Shalit, was released last October in a prisoner exchange brokered by Egypt. Challenging the practice of administrative detention, which has been used against thousands of Palestinians over time, was a more fundamental goal.

Israel says that administrative detention is essential for security, particularly in cases where exposing evidence would compromise intelligence sources. The detention orders are technically limited to six months, but they can be renewed repeatedly, and some Palestinians have been held on secret evidence for years.

As news of the agreement spread on Monday, hundreds of Palestinians took to the streets of Gaza in celebration by foot, on motorbikes and in speeding cars. Young men wandered around with trays of sweets.

In downtown Ramallah, hundreds of Palestinians held a candlelight victory march. Wafa Abu Ghulmi, the wife of a jailed leftist militant leader who has been in solitary confinement since 2010, said that where negotiations and the Shalit deal had failed, “the strike of the empty stomachs succeeded.”