CAIRO (AP) — The Egyptian military pounded Islamic militant positions and killed 23 extremists in dawn raids in Sinai on Thursday, a day after an unprecedented assault by Islamic State-linked extremists in the restive peninsula that undermined government efforts to stem an insurgency in the area despite a two-year crackdown.

The fighting — the bloodiest in the Sinai Peninsula in decades — heightened tensions across Egypt following the assassination this week of the country’s chief prosecutor in a car bombing in Cairo. President Abdel-Fattah el-Sissi on Wednesday vowed to step up the legal battle against Islamic militants.

The escalation comes on the second anniversary of the military’s ouster of Islamist President Mohammed Morsi. Also Wednesday, a special forces raid on a Cairo apartment killed nine members of Morsi’s outlawed Muslim Brotherhood, which responded by calling for a “rebellion.”

In Sinai, security officials said airstrikes killed 23 extremists in dawn raids just south of Rafah, a key Sinai border town near the Gaza Strip.

The officials also said the army was searching for extremists house to house in the town of Sheikh Zuweid — where the militants attacked a string of army checkpoints the previous day — and was demining roads in and around the area that militants had booby trapped with mines and improvised explosives devices.

The officials spoke on condition of anonymity because they were not authorized to talk to the media.

An Associated Press reporter across the border in the Gaza Strip heard explosions and saw smoke rising in the area as airstrikes continued in the afternoon and warplanes roared overhead. Two armored personnel carriers were seen maneuvering in the border area.

Militants in northern Sinai have battled security forces for years but stepped up their attacks following the 2013 military ouster of Morsi after mass protests against his rule. El-Sissi, then the nation’s army chief, led the ouster and was elected president last year.

Authorities and pro-government media have blamed much of Egypt’s recent violence on the Brotherhood, which has been branded a terrorist group. The Brotherhood denies involvement, although it and other Morsi supporters have faced a sweeping crackdown that has led to thousands of arrests, mass convictions and death sentences. Morsi is among those condemned to die, but has an appeals process ahead of him.

The latest bloodshed came as Egypt was marking the second anniversary of Morsi’s July 3 overthrow, although the celebrations were muted amid Monday’s killing of Prosecutor General Hisham Barakat and fears of unrest by the former president’s supporters.

At Barakat’s funeral Tuesday, el-Sissi pledged to bring his killers to justice. He signaled an even harsher campaign against the Brotherhood, and since then toughened anti-terrorism legislation has been submitted for his approval. El-Sissi has not addressed the public since Sinai battles erupted.

The coordinated assault by scores of extremists that focused on Sheikh Zuweid involved a wave of suicide bombings and an attack on its main police station, which they shelled with mortars and rocket-propelled grenades in a firefight with police inside that lasted most of the day, the officials said.

The army said 17 troops and over 100 militants were killed, although several senior security officials from multiple branches of Egypt’s forces in Sinai said scores more of soldiers also died in the fighting.

The main insurgent organization operating in Sinai, which calls itself the Sinai province of the Islamic State group, claimed its fighters targeted 15 army and police positions and staged three suicide bombings, two that targeted checkpoints and one that hit an officers’ club in the nearby city of el-Arish. The authenticity of the claim could not be immediately verified but it was posted on a Facebook page associated with the group.

In Wednesday’s raid on the Cairo apartment, the Interior Ministry said the nine Brotherhood members who were killed had been plotting attacks on the police, the judiciary and the media.

The Brotherhood, which called for a “rebellion” in response, called the killings “a turning point that will have its own repercussions,” adding that “it will not be possible to control the anger of the oppressed.” The move raises the prospect of some Brotherhood supporters who had previously focused on peaceful demonstrations to turn to violence.

Also Thursday, a newspaper close to the Egyptian government said the militants behind the Sinai attacks used sophisticated weaponry, including Russian-made Kornet anti-tank missiles. In a graphic on its front page, el-Watan daily said they also used mortars, anti-aircraft guns and other guided missiles.

Newspapers led their front pages with the attack, with many describing it as a “war.” Graphic photographs released by the military showed the bodies of extremists killed in the fighting who were wearing desert combat fatigues and ammunition pouches.

Late on Wednesday, a resident of Sheikh Zuweid speaking in Cairo said many civilians in the town were trapped by the fighting and military siege, with no water or electricity. He said many residents are trying to flee to el-Arish, the area’s largest city.

Also Thursday, Israeli Prime Minister Benjamin Netanyahu warned of the growing threat to the region from Islamic State militants and expressed condolences to Egypt over the deadly IS-linked attacks in Sinai.

“We see in front of our eyes IS acting with extraordinary cruelty both in our northern border and at our southern border,” he said. “Our hearts are with the Egyptian people, we send our condolences to the Egyptian government and the families of those who were killed in battle with the cruel terror.”

Egypt and Israel share a border in the Sinai and have cooperated in the past on cross-border militant threats.

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Associated Press writers Fares Akram in the Gaza Strip, Ian Deitch in Jerusalem and Aya Batrawy in Dubai, United Arab Emirates, contributed to this report.