At least seven men were killed and another 12 injured on Monday when the Israeli army blew up an attack tunnel stretching from the Gaza Strip into Israeli territory, the Hamas-run Gaza Health Ministry said in the deadliest incident in the coastal enclave since the 2014 Gaza war.

Israel’s Chanel 2 put the death toll at 11, but this was not confirmed by Hamas officials.

“The explosion took place inside Israeli territory. The majority of the dead were activists that entered the tunnel after it was exploded and died in the Gaza Strip, and not as a result of the explosion,” said an IDF spokesperson Avichay Adraee

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The IDF said the terror tunnel was discovered inside Israeli territory near the Gaza Strip and is believed to have been dug after 2014. The tunnel was being built by the Islamic Jihad terror group. It ran from the Gazan city of Khan Younis, crossed under the border for dozens of meters, and approached Kibbutz Kissufim.

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The incident significantly raised tensions in the region, with leaders of the different Palestinian terror groups meeting in Gaza in a bid to formulate a response.

Israel deployed its Iron Dome rocket interceptors in the area and declared a closed military zone near the Gaza border in case the Palestinians tried to respond with rocket fire.

“We are not interested in an escalation but we are ready for all scenarios” Adraee said.

Media reports said Islamic Jihad wanted an immediate coordinated military response, while Hamas was urging caution and coordination with Egypt in order not to jeopardize the fragile Palestinian unity deal that is supposed to be implemented over upcoming weeks.

Above: Casualties of the strike at a Gaza hospital.

Hamas called the Israeli strike a “dangerous escalation against our people” and said it was “a desperate attempt to sabotage efforts to restore Palestinian unity.”

“We affirm that resisting the occupation, in all its forms and through the use of various tools, is a natural and guaranteed right of our people,” the Hamas statement said, adding that it stood together with Islamic Jihad.

“We are brothers in jihad and comrades in martyrdom, united around the core principles of our people and its resistance.”

The Hamas-run Gaza Health Ministry said four of the dead were Islamic Jihad members, including two senior commanders, Arafat Abu Murshad, the Islamic Jihad’s central Gaza commander and his deputy Hassan Abu Hassanein. The other three others were named as Ahmad Khalil Abu Armana, 25, Omar Nasar al-Fallit, 27, and Jihad Abdullah al-Samiri, 32.

Two Hamas members, Musbah Shabir, 30 and Mujahid Mohammed Marwan Algha, were also killed during the rescue operation, Hamas said.

Islamic Jihad also threatened revenge.

“This is a massacre,” said senior Islamic Jihad leader Khaled al-Batash. “All our options are open. We will take all considerations into account, but we will not allow the enemy to set the rules of engagement.”

“The Zionist terror government must realize that we will not hesitate to protect our people and our land,” Islamic Jihad spokesman Dawood Shehab said on Twitter, adding that the terror group “is considering all of its options,” including the “option of responding to this aggression.”

Islamic Jihad is the second-largest terror group in Gaza after Hamas.

Prime Minister Benjamin Netanyahu and Defense Minister Avigdor Liberman hailed the IDF for destroying the attack tunnel, with the two leaders attributing its discovery to Israel’s new “breakthrough technology.”

In remarks at the weekly Likud faction meeting, the prime minister said the long-rumored advanced technology to locate the attack tunnels had been utilized in the recent operation.

“I told you many times before that we are developing breakthrough technology to deal with the tunnel threat,” said Netanyahu at the start of the meeting. “We are implementing it. Today, we located a tunnel and we destroyed it.”

The prime minister said Israel holds Hamas responsible for all military action against Israel emanating from the Gaza Strip and “whoever hurts us, we hurt them.”

Earlier, the military said the tunnel had been under surveillance for an extended period of time and was under active construction at the time of the demolition.

“The tunnel was detonated from within Israel, adjacent to the security fence,” the military said in a statement.

IDF spokesperson Lt. Col. Jonathan Conricus said the tunnel was at least two kilometers (1.25 miles) away from the kibbutz and did not pose a threat to its residents. Liberman also said no Israelis were endangered by the tunnel.

The demolition was carried out near the fence separating Israel from Gaza, on the Israeli side.

The destruction of the tunnel was first reported by Palestinian media on Monday afternoon. The reports said it was carried out by airstrike.

The IDF initially contradicted those reports, saying it was a “controlled demolition,” but Conricus later clarified that the military would not comment on what munitions were used.

The IDF officers said it was not immediately clear who dug the tunnel, but that ultimately the Israeli army holds Hamas “accountable and responsible,” as it is the governing figure in the Strip.

Avi Issacharoff contributed to this report.