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.

Top officials from the United States, Russia, United Nations and European Union will meet Monday to discuss deadlocked efforts to end the Israel-Palestinian conflict, the U.N. said.

It will be the first top level meeting of the diplomatic Quartet in six months and comes amid a new flare-up in violence which has left at least 21 Palestinians dead in Israeli raids on the Gaza Strip since Friday.

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.

United Nations Interim Force in Lebanon spokesman Neeraj Singh stated on Monday that the situation in southern Lebanon is calm and stable, reported the National News Agency.

He denied that any unusual activity was taking place in the South, particularly at Kfarkila.

Hizbullah on Sunday claimed that “there are some March 14 associates in power who are involved in facilitating arming and infiltration into Syria,” describing the U.S. embassy in Lebanon as “a military operations room against Syria.”

“The countries that conspired against Syria have admitted that they had engaged in an uncalculated adventure and nowadays we’re noticing how they have started tactical, political retreats,” Sheikh Nabil Qaouq, deputy head of Hizbullah’s Executive Council, said.

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."

The United States expressed concern Saturday over deadly violence between Israel and Palestinians across the Gaza border and urged both sides to restore calm.

"We are deeply concerned by the renewal of violence in southern Israel," said State Department spokeswoman Victoria Nuland in a statement. "We call on both sides to make every effort to restore calm."

Defense Minister Ehud Barak warned on Saturday that Israel will continue to hit Palestinians who attack its citizens, after air strikes on Gaza left 15 Palestinians dead.

Israeli air strikes on Gaza killed 15 Palestinians, including a militant group chief, medics said on Saturday, in the deadliest 24 hours in the border area in more than three years.

A Palestinian riding a motorcycle was killed and two others were wounded in an Israeli air raid close to the southern town of Rafah near the border with Egypt on Saturday afternoon, Palestinian medics said.

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.