Smoke rises following Israeli missile strikes on Gaza City, May 13

Israel fired artillery and mounted extensive air strikes on Friday against a network of Palestinian militant tunnels under Gaza that it dubbed “the Metro”, amid persistent rocket attacks on Israeli towns.

An Israeli military spokesman said that while ground forces had taken part in the 40-minute, pre-dawn offensive, none had crossed into the Gaza Strip, as hostilities entered their fifth day with no sign of abating.

Health officials in northern Gaza said a woman and her three children were killed during the Israeli operation and that their bodies were recovered from the rubble of their home.

Rocket barrages against southern Israel swiftly followed the Israeli strikes, which the spokesman said included artillery and tank fire from inside Israeli territory.

The most serious fighting between Israel and Gaza militants since 2014 began on Monday after the enclave’s ruling Hamas group fired rockets at Jerusalem and Tel Aviv in retaliation for Israeli police clashes with Palestinians near al-Aqsa mosque in Jerusalem.

At least 119 have been killed in Gaza, including 31 children and 19 women, and 830 others wounded in the current hostilities, Palestinian medical officials said.

The death toll in Israel stood at eight: a soldier patrolling the Gaza border, six Israeli civilians - including a an elderly woman who fell on the way to a shelter on Friday and two children - and an Indian worker, Israeli authorities said.

In northern and eastern parts of Gaza, the sound of artillery fire and explosions echoed early on Friday. Witnesses said many families living near the border left their homes, some seeking shelter at United Nations-run schools.

Lieutenant Colonel Jonathan Conricus, an Israeli military spokesman, said 160 aircraft as well as artillery and armoured units, "not inside the Gaza Strip", had taken part in what he called the largest operation against a specific target since the fighting began.

"What we were targeting is an elaborate system of tunnels that spans underneath Gaza, mostly in the north but not limited to, and is a network that the operatives of Hamas use in order to move, in order to hide, for cover," he said in a briefing to foreign reporters.

"We refer to (it) as the Metro," he said, adding that a final assessment on the outcome of the operation was pending.

Israeli Prime Minister Benjamin Netanyahu said on Thursday the campaign "will take more time". Israeli officials said Hamas, Gaza's most powerful militant group, must be dealt a strong deterring blow before any ceasefire.

U.S. President Joe Biden called on Thursday for a de-escalation of the violence, saying he wanted to see a significant reduction in rocket attacks.

TENSIONS IN ISRAEL

The hostilities have fuelled tension between Israeli Jews and the country's 21% Arab minority who live alongside them in some communities.

Violence continued overnight in mixed communities of Arabs and Jews. Over the past several days, synagogues were attacked and fighting broke out on the streets of some towns, prompting Israel’s president to warn of civil war.

On Thursday, the Israeli military said it was building up forces on the Gaza border, raising speculation about a possible ground invasion, a move that would recall similar incursions during Israel-Gaza wars in 2014 and 2009.

But an invasion looked unlikely, given Israel's reluctance to risk a sharp increase in military casualties on Hamas turf.

The U.N. Security Council will publicly discuss the worsening violence between Israel and Palestinian militants on Sunday, diplomats said after the United States had objected to a meeting on Friday.

Truce efforts by Egypt, Qatar and the United Nations had yet to deliver a sign of progress.

The Israeli military has put the number of militants killed in Israeli attacks at between 80 and 90. It said that so far, some 1,800 rockets have been fired at Israel, of which 430 fell short in the Gaza Strip or malfunctioned.

On the Israeli political front, Netanyahu’s chances to remain in power after an inconclusive March 23 election appeared to improve significantly after his main rival, centrist Yair Lapid, suffered a major setback in efforts to form a government.