Israeli air strikes on Gaza killed three senior Islamic Jihad commanders and at least nine civilians, including four children, on Tuesday, Palestinian officials said, in an operation that drew an immediate threat of retaliation from the militant group.

The air strikes were the latest incident in more than a year of surging violence that has seen repeated Israeli military raids and escalating settler violence in the occupied West Bank, amid a spate of Palestinian street attacks against Israelis.

Hours after the Gaza operation, military forces raided the West Bank city of Nablus, one of the focal points of months of confrontation between Israeli troops and Palestinian fighters.

Last week brought a bout of cross-border fire after the death in Israeli detention of an Islamic Jihad hunger striker.

Israel said it targeted three leaders of Islamic Jihad, an Iranian-backed group that is on terrorism watchlists in the West and which commands the second-biggest armed network in Gaza.

Any major escalation could hinge on whether the enclave’s ruling Hamas militants join in. Such participation would make Hamas leader targets for assassination, Israeli security cabinet minister Israel Katz told Tel Aviv radio station 103 FM.

In another sign Israel was preparing for a flare-up, its foreign minister, Eli Cohen, said he would return early from a visit to India after meeting Prime Minister Narendra Modi.

Islamic Jihad spokesperson Tareq Selmi said Israel’s “crime will not pass unpunished”.

“The bombardment will be met by bombardment and the attack will be met by an attack,” he said.

A Gaza health official said at least 12 people had been killed and 20 wounded in the strikes that hit residential areas in the densely populated strip in which 2.3 million Palestinians live on a patch of 365 square kilometres (140 square miles).

An Israeli military spokesman said the army was looking into reports of civilian deaths but had no immediate comment.

“We’re aware of some collateral and we’ll learn more as the day goes ahead,” he told a briefing with reporters.

Islamic Jihad identified the commanders killed as Jihad Ghannam, Khalil Al-Bahtini and Tareq Izzeldeen.

The military said 40 jets took part in what it called “precise” strikes. “It was a convergence of intelligence, timing and weather,” a military spokesperson said.

Ten weapons and infrastructure manufacturing sites, including rocket production workshops and a site for making concrete used for tunnels, as well as military compounds belonging to the group were also hit, the spokesperson said.

Reservists call up

Videos circulating on social media that Reuters could not immediately verify showed a convoy of armoured Israeli military vehicles arriving in Nablus as children walked along the street carrying their school bags.

But Gaza remained relatively quiet as residents inspected the damage and prepared to bury their dead.

Israeli military spokesperson Brigadier-General Daniel Hagari said objectives in Gaza had been achieved. A limited call-up of military reservists had also been approved.

Hamas chief Ismail Haniyeh, who has been splitting his time between Turkey and Qatar, said in a statement: “Assassination of leaders will not bring the occupation security but more resistance.”

Videos showed billowing smoke and flames that lit up the night sky as trucks of firefighters sped to a building that had been hit, while a medic reassured a young girl who appeared confused.

“Your family is all safe, don’t worry,” he said.

During the bombardment, Palestinians took to social media to mourn a well-known dentist who was killed at home with his wife in Tuesday’s air strikes, describing him as a loyal friend and humble man.

Last week, the death of Khader Adnan in Israeli custody following an 87-day hunger strike triggered several hours of cross-border fighting between Israel and armed groups in Gaza, in which one Palestinian was killed.

More than 100 Palestinians and at least 19 Israelis and foreigners have been killed in the strife since January.

The Palestinian foreign ministry strongly condemned Israel’s attack and said a negotiated political solution was the only way to achieve security and stability. Islamic Jihad, like Hamas, refuses coexistence with Israel and preaches its destruction.

Israel captured Gaza and the West Bank, areas that Palestinians want for an independent state with East Jerusalem as its capital, in a 1967 war.

COGAT, a unit of the Israeli defence ministry that coordinates civilian affairs with Palestinians in occupied territories, said its two Gaza crossings were closed to people and goods until further notice.

In anticipation of rocket fire in response to the killings, Israel’s military urged citizens living in towns within 40 km (25 miles) of Gaza to stay near bomb shelters from 2:30 a.m. on Tuesday until 6 p.m. on Thursday.