The announcement came shortly after Egypt, which has been trying to broker the truce for months, said the cease-fire would go into effect on Thursday. Israel refused to confirm a deal, but said a "new reality" would take hold if Palestinian attacks end.
In a last-minute jolt, Israeli aircraft attacked three targets in the southern Gaza Strip. One of the airstrikes destroyed a car, killing five 'militants' inside. A large crowd gathered around the car's smoldering remains.
Hamas officials accused Israel of trying to undermine the truce, but said they would not let the violence derail the Egyptian efforts.
"We are going to commit ourselves to the start time that Egypt is going to declare regarding the calm," said Hamas spokesman Sami Abu Zuhri. However, the group's television station said the movement would respond to "any Zionist aggression," underscoring the delicate situation.
Egypt's powerful intelligence chief, Omar Suleiman, has been meeting separately with Israeli and Hamas officials for months in hopes of brokering a truce.
Israel has been seeking a halt to rocket attacks launched from Gaza nearly every day, an end to Hamas' weapons buildup, and the release of an Israeli soldier held by Hamas for two years.
Hamas, meanwhile, wants an end to Israel's military activity in Gaza and the lifting of an Israeli blockade that has caused widespread destitution in the already impoverished coastal strip.
The state-run Egyptian news agency MENA cited an unidentified high-level Egyptian official as saying both sides "have agreed on the first phase" of an Egyptian-mediated package to end the violence in Gaza.
It said the first phase would be a "mutual and simultaneous calm" in the Gaza Strip beginning at 6 a.m. Thursday (0300 GMT).
"Egypt hopes that the two sides will exert all efforts to bring the calm to a success," the agency quoted the official as saying.
An Egyptian official told The Associated Press that if the area is quiet for three days, Israel would begin to open Gaza's border crossings to let more humanitarian supplies into the area. A week later, Israel would allow in additional goods.
The official said in a final phase Israel would consider reopening Gaza's border crossing with Egypt. The Rafah crossing is the main route for Gaza's 1.4 million people to leave the area. Israel and Egypt closed the crossing in June 2007 after Hamas violently seized control of Gaza, a move that has confined the vast majority of Gazans inside the coastal strip for the past year.
The deal is meant to last for six months, he said, and includes the possibility of extending a truce to the West Bank, where Israeli regularly conducts arrest raids targeting militants.
A Hamas official said the Rafah deal would be connected to the release of the Israeli soldier, Cpl. Gilad Schalit, who was captured by Palestinian militants in a cross-border raid two years ago. Israel has balked at Hamas' demand for a release of hundreds of militants held in Israeli jails.
The Egyptian and Hamas official both spoke on condition of anonymity, saying they were not permitted to go on the record with the information.
Israeli government spokesman Mark Regev would not confirm or deny a deal.
"What is important is not only words but deeds. If there is a total absence of terror attacks from Gaza into Israel and if there is an end to arms buildup in Gaza Strip and movement on the hostage Gilad Schalit that will indeed be a new reality."
A Hamas official said talks on Schalit would begin after the initial three days of quiet. Israeli defense officials said they expect negotiations on the soldier to begin on Sunday, an apparent confirmation of the truce's conditions.
Hamas has ruled Gaza with an iron fist, and the cease-fire is expected to include other Palestinian groups. Khaled al-Batch of the Islamic Jihad, a small Iranian-backed group responsible for much of the rocket fire, said his faction would be "committed to this calm as much as the occupation is committed."
Iranian-backed Gaza militants have been bombarding southern Israel with rockets and mortars for seven years. The rate of fire increased after Israel pulled its troops and settlers out of Gaza in 2005 and stepped up further last year after Hamas wrested power from forces loyal to moderate Palestinian President Mahmoud Abbas.
Israel has responded with pinpoint air and ground attacks that have killed hundreds of Palestinians, many of them civilians. It has also imposed a strict blockade on Gaza, letting in only limited amounts of humanitarian aid, restricting fuel supplies and widening already rampant unemployment. Ending the economic sanctions by opening Gaza's crossings with Israel and Egypt has been a major Hamas demand in the cease-fire talks.
Although the Rafah crossing lies on the Gaza-Egypt border, Europeans monitoring the passage require Israeli security clearance to operate. That clearance has not been given since Hamas took over Gaza.
Much skepticism has surrounded the talks, and not only because past accords — most recently, a November 2006 deal — have broken down fairly quickly.
Israel is suspicious of Hamas' motives, especially since the militant group has declared it would take advantage of any lull to rearm. Israel also is reluctant to legitimize Hamas' rule in Gaza through a truce agreement. Hamas rejects the existence of a Jewish state and has killed more than 250 Israelis in suicide bombings.
But with the Israeli government under heavy domestic pressure to halt the rocket fire, the choices were a truce or a broad invasion of Gaza.
Israel has been reluctant to launch an offensive in Gaza, fearing heavy casualties in the crowded urban environment.
