GAZA CITY (AP) ― Egypt has mediated a cease-fire between Palestinian militant factions and Israel after four days of violence, an Egyptian security official said.

The official told the Associated Press that a cease-fire went into effect at 1 a.m. Tuesday. He spoke on condition of anonymity because of the sensitivity of the issue. It was not immediately clear when a formal announcement of a cease-fire would be made.

The official said that after hours of talks, the Palestinians agreed to stop launching rockets at southern Israeli cities and Israel agreed to stop targeting militants in airstrikes.

Neither Palestinian militant groups or Israel would immediately comment. There were no reports of violence by either side.

The fighting was triggered by Israel’s killing of a militant leader last week. Twenty-four Palestinians died, including seven on Monday, and about 1 million Israelis in rocket range have seen their lives disrupted by the threat of rocket attacks, with frequent sirens warning them to run for cover.

Earlier, Egyptian cease-fire efforts had appeared to stall.

Israeli Prime Minister Benjamin Netanyahu had warned that Israel would keep striking those trying to harm Israeli civilians and that Israel was “ready to broaden its operation.’’

Gaza militants insisted that Israel stop firing first and that it promise to halt airstrikes aimed at killing Gaza militants for good ― a guarantee Israel is unlikely to give.

Meanwhile, government officials and missile experts in Israel praised the performance of Iron Dome, an Israeli-made system designed to shoot down short-range rockets like those fired from Gaza.

Iron Dome has been rolled out over the past year, and the current fighting poses its most serious test. Israel has other systems deployed against longer-range missiles.

Iron Dome uses cameras and radar to track incoming rockets and intercepts only those that would pose a threat to people and property, ignoring those that are expected to fall in open areas.

The military said that of 143 rockets fired since Friday, it tried to intercept 63 and succeeded in all but nine of those attempts. No Israelis have been killed in the current fighting, and property damage has been relatively minor.

Uzi Rubin, a missile expert and former Defense Ministry official, said Iron Dome has exceeded expectations. “The performance up to now has been almost flawless,’’ Rubin said, adding that the perception could change quickly in the event of casualties.

Military analyst Yiftah Shapir said Iron Dome would likely score fewer interceptions if Israel were attacked by a larger number of missiles simultaneously, a scenario Israel would have to consider if it attacks Iran over its nuclear program. Tehran’s proxies on Israel’s borders ― the Lebanese Hezbollah militia, along with Hamas and Islamic Jihad in Gaza ― are believed to have a stockpile of tens of thousands of rockets and missiles.

Shapir said Iron Dome has given a psychological boost to those living in rocket range, but it has not reduced the economic damage caused by closing schools and keeping hundreds of thousands of people from their jobs and daily routines.

Others noted that each intercept costs about $100,000, arguing that the cost could be prohibitive if Israel were fighting a full-fledged war.

On the Gaza side, the Islamic Jihad, the second largest militant group in Gaza, has taken the initiative.

Islamic Jihad has maintained close ties to its sole sponsor, Iran, while rival Hamas in recent months has drifted away from its longtime patron, in part because of disagreements over Syria’s brutal crackdown on regime opponents. Iran has punished Hamas for refusing to side with Syrian President Bashar Assad, including by cutting funding.

Israeli officials believe that Islamic Jihad has amassed hundreds of rockets and missiles, if not thousands, including weapons taken from Libyan military bases during the chaos surrounding the fall of Libya’s longtime ruler, Moammar Gadhafi. Missiles and other weapons reach Gaza through smuggling tunnels running under its border with Egypt.

In the current round, Islamic Jihad showed that the three main cities in southern Israel ― Ashkelon, Ashdod and Beersheba ― are in easy reach of its Russian-designed Grad rockets.

On Monday, two dozen rockets struck southern Israel, including one that damaged an empty preschool on a communal farm. Police said no one was hurt.

Rubin believes Islamic Jihad also has longer-range missiles that could reach the major population centers of central Israel, like Tel Aviv.

Hinting at possible escalation, Islamic Jihad warned Monday that its “patience is limited’’ and that it is ready to unleash “fire and destruction,’’ though such rhetoric is routine during flare-ups like this one.

Hamas, which has ruled Gaza since a 2007 takeover, has pointedly kept out of the fighting and is appealing for calm, though it has not prevented rocket fire by Islamic Jihad and the Popular Resistance Committees.

Hamas is trying not to provoke a major Israeli offensive that could undermine its control of the territory of 1.7 million Palestinians. An Israeli offensive three years ago delivered a damaging blow.

``Hamas is behaving like a responsible government in Gaza,’’ said Fawaz Gerges of the London School of Economics.