Israel’s Defence Minister Yoav Gallant has told community leaders in southern Israel to prepare for the possibility of a prolonged conflict, after strikes on the Gaza Strip on Tuesday morning.
The attack killed three senior figures in Palestinian Islamic Jihad and 10 civilians, including women and children.
The so-called Joint Operations Room of militant organisations in Gaza has warned Israel will “pay the price” for the country’s attacks on the enclave.
The Shaar HaNegev Regional Council in Israel says 200 families are expected to evacuate the area by the end of Tuesday, due to fears of potential rocket attacks from Gaza.
The Palestinian Authority earlier warned of “a dangerous escalation that threatens an overall explosion” after the Israeli strikes, which the country has called Operation Shield and Arrow.
As well as the commanders, munitions and production sites were targeted.
The Al-Quds Brigades, the armed wing of Palestinian Islamic Jihad, also said three of its commanders had been killed, along with their wives “and a number of their children”.
Israeli President Isaac Herzog praised the attacks, congratulating the military on "comprehensive and intensive operations to foil terror and defend the State of Israel”.
Lebanon’s Hezbollah called the strikes “barbaric” and a “crime against humanity,” according to Lebanese broadcaster Al Mayadeen.
Witnesses told AFP that bombing began in Gaza at 2am and continued for two hours.
Gaza resident Waseem told The National that he was “surprised” at the escalation, as there were no immediate “skirmishes that preceded the strikes”.
“None of us know what today will be like, and whether we should continue in our daily routines or not,” he said.
The Palestinian Authority Foreign Ministry said it held the Israeli government “fully and directly responsible” for what it described as “a dangerous escalation that threatens an overall explosion”, Palestinian news agency Wafa reported.
Later on Tuesday, an Israeli strike on a car in the southern Gaza Strip's Khan Younis city killed two people. The Israeli military confirmed the attack, saying the vehicle had been carrying anti-tank missiles.
The attacks come days after a brief increase in violence between Gaza and Israel, following the death in Israeli custody of high-profile Palestinian hunger striker Khader Adnan, who Israel had accused of being a senior terrorist leader.
Militants in Gaza fired 104 rockets towards Israel in the exchange, injuring three and damaging property. One Palestinian was killed in subsequent Israeli strikes.
The Palestinian Islamic Jihad said it would respond to the latest bombings with attacks of its own, while Hamas said “the occupation is escalating its aggression against the Gaza Strip and targeting those who are safe in their homes”.
Israelis were put on alert in the hours before the attack.
They were instructed “to remain in the vicinity of a designated shelter” within 40km of the Gaza border, according to the National Emergency Portal, an online service.
Authorities also closed beaches in areas close to Gaza and a hospital said it had started moving patients to fortified wards.
Israel's military named Khalil Bahitini, Jahed Ahnam and Tarek Azaldin as the senior PIJ commanders killed.
Palestinian health officials have also said that a 14-year-old boy was shot and wounded during an Israeli raid on the West Bank city of Nablus on Tuesday morning.
Footage later circulated showing an Israeli military jeep hitting an improvised explosive device. Nablus-based armed group Lion's Den claimed responsibility for the detonation. One Israeli soldier was lightly wounded.
Israeli authorities said that they foiled separate potential stabbing attacks on Tuesday in the West Bank town of Hawara and the Old City of Jerusalem.
The Gaza strikes have been welcomed by a number of high-profile Israeli politicians, including senior members of the opposition.
Israeli Defence Minister Yoav Gallant said “any terrorist who harms Israeli citizens will be made to regret it”. The minister also permitted Israel's military to call up reservists in anticipation of further escalation.
Opposition leader Yair Lapid said he supported the bombings.
“Terror groups in Gaza know that the intelligence community and the security forces are following their every move and every step and the score will be settled,” said Mr Lapid.
Prime Minister Benjamin Netanyahu simply tweeted a picture of the three dead suspected militants, saying “shield and arrow”, in reference to the military operation's name.
In a sign of growing tensions with Mr Netanyahu's cabinet over the government's security policies in recent months, Israeli outlet Ynet reported that details of the operation were held from far-right National Security Minister Itamar Ben-Gvir, amid fears among senior government figures that he would leak details of the strikes.
Mr Ben-Gvir has been calling for harsher Israeli responses in Gaza in recent weeks and hailed Tuesday's strikes as a “good start”.
His Otzma Yehudit party has been boycotting parliamentary sessions in protest. The party said it was ending its boycott following the strikes.
The office of Israel's attorney general said that Mr Netanyahu had been authorised by the body to launch the operation without convening the cabinet.
The prime minister is due to hold a security assessment to discuss next steps.
Israeli Foreign Minister Eli Cohen cut short a visit to India as part of a business delegation.
General Secretary of the Gulf Co-operation Council Jassem Mohamed Al Budaiwi condemned the Israeli escalation on Gaza and its raid in the city of Nablus. Mr Al Budaiwi expressed his "vehement disapproval" over the violence which the GCC considers a "major violation by the occupation forces".
Tuesday's strikes are the latest incident in more than a year of surging violence, marked by repeated Israeli military raids, escalating settler violence in the occupied West Bank and a spate of Palestinian street attacks.
More than 90 Palestinians and at least 19 Israelis and foreigners have been killed since January.
