Relentless rocket fire and rioting in mixed Jewish-Arab towns fuelled growing fears Wednesday that violence between Israel and Palestinians that has claimed 50 lives could spiral into "full-scale war".
Palestinian militants have launched more than 1,000 rockets since Monday, said Israel's army, which has launched hundreds of air strikes on Hamas and other Islamist groups in the crowded costal enclave of Gaza.
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The most intense hostilities in seven years have killed at least 43 people in Gaza, including 13 children, two Palestinians in the West Bank, and five Israelis, triggered by weekend unrest at Jerusalem's Al-Aqsa mosque compound, which is sacred to both Muslims and Jews.
As world powers voiced growing alarm and the UN Security Council readied for another emergency meeting on the bloody crisis, the UN Middle East envoy Tor Wennesland warned that "we're escalating towards a full-scale war".
"Leaders on all sides have to take the responsibility of de-escalation," he said, echoing warnings from the international community.
Israeli Prime Minister Benjamin Netanyahu declared a state of emergency in the mixed Jewish-Arab Israeli city of Lod, where police said "wide-scale riots erupted among some of the Arab residents".
There were fears of widening civil unrest as protesters waving Palestinian flags burnt cars and properties, clashed with Israeli police and attacked Jewish motorists in several mixed Jewish-Arab towns across Israel.
Palestinian groups, mostly Hamas and Islamic Jihad, have launched more than 1,000 rockets, Israel's army said, including hundreds at Tel Aviv, where air sirens wailed overnight.
Of these, 850 rockets have hit in Israel or been intercepted by Israel's Iron Dome air defence system, while the rest have crashed inside Gaza, he said.
Israel has launched hundreds of air strikes at Gaza, the Israeli-blockaded coastal enclave of two million people that Hamas controls, targeting what the army described as Palestinian military sites.
Aside from the mounting death toll, at least 230 Palestinians were wounded, many rescued from the smouldering ruins of buildings. On the Israeli side, more than 100 people have been injured, as residents across the Jewish state have been ordered to seek shelter.
British Prime Minister Boris Johnson on Wednesday urged Israel and the Palestinians to "step back from the brink", calling for both sides to "show restraint".
The chief prosecutor of the International Criminal Court, Fatou Bensouda, voiced concern at the escalation of violence and said "crimes" may have been committed.
Bensouda announced on March 3 that she had opened a full investigation into the situation in the Israeli-occupied territories, infuriating Israel, which not a member of The Hague-based court.
Israeli Defence Minister Benny Gantz warned Tuesday that "this is just the beginning" of Israel's strikes, vowing that the operation, now dubbed "Guardian of the Walls", would aim to restore peace "for the long-term".
Hamas leader Ismail Haniyeh vowed in turn to step up its operation code-named "Sword of Jerusalem", warning that "if Israel wants to escalate, we are ready for it".
Israeli army spokesman Jonathan Conricus said he expected the fighting to intensify and, when asked about unconfirmed reports that Hamas might seek a ceasefire, said: "I don't think my commanders are aware, or particularly interested."
In Gaza City, people sifted through debris after an Israeli air strike destroyed a 12-storey building near the coastline.
Hamas said the tower block had been a residential building. AFP reporters said it also housed the offices of several Hamas officials.
Five members of a single family were killed by an Israeli strike in northern Gaza on Tuesday, including young brothers Ibrahim and Marwan, who were filling sacks of straw at the time.
"We were laughing and having fun when suddenly they began to bomb us. Everything around us caught fire," their cousin, also called Ibrahim, told AFP.
"I saw my cousins set alight and torn to pieces," said the 14-year-old, breaking down in tears.
In Israel's central city of Lod, a man and a girl were killed Wednesday by rocket fire from Gaza. Israel's foreign ministry identified one of the dead as 16-year-old Nadin Awad, an Arab Israeli.
Her cousin, Ahmad Ismail, told public broadcaster Kan that he was near Nadin when she was killed alongside her father Khalil Awad, 52.
"I was at home, we heard the noise of the rocket. It happened so quickly. Even if we had wanted to run somewhere, we don't have a safe room," Ismail told Kan.
Earlier, an Israeli woman was killed as rockets hit Rishon Letzion on the coastal city's southern edge, and in Ashkelon near Gaza, which Hamas threatened to turn into "hell", rockets fired by militants killed two women.
The crisis started last Friday when weeks of tensions boiled over and Israeli riot police clashed with crowds of Palestinians at Jerusalem's Al-Aqsa mosque, on the last Friday of the Muslim holy month of Ramadan.
Nightly clashes since then have rocked the ancient compound and flared elsewhere in east Jerusalem, leaving more than 900 Palestinians injured.
Palestinians clashed again with Israeli officers in riot gear on Tuesday evening, with 245 Palestinians injured, according to the Palestinian Red Crescent.
Large protests were held Tuesday in solidarity with Palestinians around the world, including in London, as well as in Muslim-majority countries including Kuwait, Oman, Pakistan, Tunisia and Turkey.