Israel's assassination of a top Gaza militant, which brought hundreds of rockets raining down on the Jewish state and the danger of further escalation, has left some wondering if its policy of targeted killings is still effective.

Since Friday, when an Israeli air strike killed Zuhair al-Qaisi, head of the Popular Resistance Committees, 23 Palestinians have been killed, most of them militants, prompting armed groups to fire more than 200 rockets at southern Israel, confining a million people to bomb shelters.

Former Prime Minister Saad Hariri noted on Monday that the latest “massacre committed by the Syrian regime” in Homs coincided with the Israeli assault on Gaza over the weekend.

He said in a statement: “The latest massacre committed by the regime of Syrian President Bashar Assad against innocent people not only condemns the regime, but the international community for its lack of humanity.”

China on Monday urged Israel to stop air raids on Gaza and called on both sides for an immediate ceasefire after Israeli Premier Benjamin Netanyahu vowed no let-up against rocket-firing militants.

Israel launched another spate of air strikes earlier Monday, bringing the death toll in Gaza to 20 in three days of tit-for-tat violence that began with Israel's killing of a senior militant on Friday.

Israel will continue air strikes against Gaza "as long as necessary," Prime Minister Benjamin Netanyahu said on Sunday, giving no indication that a ground operation was likely for now.

"We extracted a high price from them and will continue to do so," he said at the start of the weekly cabinet meeting. "We will act as long as necessary."

An Israeli air strike on the Gaza Strip killed the head of the Popular Resistance Committees militant group Friday, the movement said.

The PRC said General Secretary Zohair al-Qaisi was one of two Palestinians killed in the strike, along with fellow-member Mahmoud Halani, hours after Palestinians fired mortar rounds into Israel.

Israeli forces engaged in a firefight overnight with gunmen who infiltrated from Egypt's Sinai peninsula, killing one, the Israeli military said on Tuesday.

"Soldiers patrolling along the Israel-Egypt border identified a number of suspects who had infiltrated into Israel," the military said in a statement.

Rockets fired from the Hamas-ruled Gaza Strip slammed into southern Israel on Saturday without causing casualties or damage, a police spokesman said.

"Two rockets were fired and landed in uninhabited areas near the town of Sderot," spokesman Micky Rosenfeld said.

Israeli warplanes launched two air strikes on the Gaza Strip early Friday, the military said; hours after Palestinian militants fired two rockets at southern Israel.

"Israeli army aircraft thwarted an attempt by a terrorist squad to fire rockets at Israel from the northern Gaza Strip," an army statement said.

Egypt is to provide 22 megawatts of electricity to the Israeli-blockaded Gaza Strip, where the sole power plant has shut down after running out of fuel, the electricity minister said on Tuesday.

Egypt "will begin boosting the Gaza Strip with around 22 megawatts of electricity at the start of next week, to confront the crisis there and ease the suffering of the Palestinian people," Hassan Yunes said.

Three people were wounded early Sunday morning in an Israeli air strike on Gaza, medical sources said, hours after another strike injured one man.

According to the sources, the latest air strike, which targeted a home in the al-Tufah neighborhood in Gaza City, left the three in moderate condition.