At least 21 people have died in Gaza as a campaign of Israel air raids enters its fourth day, following reports of three more killings on Monday, including that of a 15-year-old boy, according to Palestinian officials.

Monday’s missile attacks also wounded 35 Gazans, while another raid on the city of Khan Younis left two people dead.

BBC reported that at least 65 people have been wounded in Gaza since the Israeli bombardment began on Friday.

Two members of the al-Quds Brigades, the military arm of the Palestinian verson of Islamic Jihad were reportedly killed in the latest Israeli missile attacks.

The Israeli military earlier confirmed that its forces carried out strikes that targeted a weapons storage facility and four rocket launching sites in the northern Gaza Strip, as well as a rocket launching site in the southern Gaza Strip.

In response to the latest wave of Israeli strikes, Palestinian fighters launched 11 rockets into Israel on Sunday night, according to Israeli sources.

Israel claimed it launched the attack to retaliate for prior rocket launches onto its territory by militants in Gaza.

According to al-Jazeera, after an apparent ceasefire agreement collapsed on Sunday, Egypt is desperately seeking to establish a truce between Israel and the militants of Gaza, on behalf of Hamas, which governs the territory.

Islamic Jihad is generally loyal to Hamas, but frequently operates independently of it.

Islamic Jihad [is] reluctant to abide by any negotiated truce unless they can get a guarantee from Israel that those assasination attacks will stop, and frankly I don’t think that guarantee is going to come,” said an al-Jazeera correspondent.

On the Israeli side, the attitude is just as intransigent.

Prime Minister Benjamin Netanyahu said on Sunday that the military strikes on Gaza will continue as long as necessary.

Meanwhile, the so-called “Quartet on the Middle East” -- the U.S., Russia, European Union and the Unitd Nations –-- will meet on Monday for the first time in six months to discuss the stalled Israel-Palestinian peace process.

Riyad Mansour, the Palestinian ambassador to the UN, demanded that the UN Security Council act immediately to stop the bloodshed.

He warned that if Israel is not held accountable this will only ensure the bolstering of its impunity and the further escalation of its crimes against the Palestinian people with far-reaching consequences for the future of our people and the prospects for peace and stability to ever be realised.