The Palestinian militant group, which still holds 59 of the 250 or so hostages seized in its October 7, 2023, attack on Israel, accused Israel of breaching the ceasefire and jeopardising efforts by mediators to secure a permanent truce.
Israeli Prime Minister Benjamin Netanyahu said he had told the military to take "strong action" against Hamas in response to the group's refusal to release the remaining hostages and because of their rejection of ceasefire proposals.
The Israeli military described the attacks as a "pre-emptive offensive" aimed at thwarting Hamas' ability to launch attacks against Israel and to rebuild and rearm its forces.
It said it targeted "mid-ranking military commanders, leadership officials and terrorist infrastructure" belonging to Hamas.
Among those killed in air strikes on their homes were Essam Addalees, the de facto head of the Hamas government, Ahmed Al-Hetta, deputy justice minister and Mahmoud Abu Watfa, the deputy minister of interior and head of the Hamas-run security services, Hamas said.
Egypt, one of the mediators in the ceasefire deal agreed in January, called for restraint and urged all parties to work towards a lasting agreement.
Israel's intense pressure on Hamas came as tensions flared elsewhere in the Middle East, which has seen the Gaza war spread to Lebanon, Yemen and Iraq.
Israeli media said Israel was opening shelters in multiple areas in commercial hub Tel Aviv to prepare for possible retaliation from Hamas or Yemen.
The Gaza attacks were far wider in scale than the regular drone strikes Israel has said it has conducted recently against suspected militants, and follow weeks of failed efforts to agree an extension to the truce agreed on January 19.
Gaza's Hamas-run health ministry said 404 people had been killed in one of the biggest single-day tolls since the war erupted.
The health ministry said many of the dead were children, and 562 people were injured.
Israel has halted aid deliveries into Gaza for more than two weeks, exacerbating a humanitarian crisis.
The Israeli military said its attacks would extend beyond air strikes, raising the prospect that Israeli ground troops could resume fighting.
As Israel launched its operation in Gaza, its forces have pressed on with an operation in the occupied West Bank that the military says is aimed at Iranian-backed militant groups in long-standing refugee camps.
Israeli jets have also struck targets in southern Lebanon and Syria in recent days as the military builds on gains it made during months of fighting against the Iranian-backed Hezbollah and during the collapse of the former Syrian regime.
Negotiating teams from Israel and Hamas had been in Doha as mediators from Egypt and Qatar sought to bridge the gap between the two sides after the end of an initial phase in the ceasefire, in which 33 Israeli hostages and five Thais were released in exchange for some 2000 Palestinian prisoners.
With the backing of the United States, Israel had been pressing for the return of the remaining hostages in exchange for a longer-term truce until after the Muslim fasting month of Ramadan and the Jewish Passover holiday in April.
However, Hamas has insisted on moving to negotiations for a permanent end to the war and a full withdrawal of Israeli forces, under the terms of the original ceasefire agreement.
On Tuesday, Hamas spokesman Abdel-Latif Al-Qanoua told Reuters communication with mediators was ongoing and the group was keen to complete the implementation of the original Gaza ceasefire deal.
Egyptian mediators said they were surprised by the overnight air strikes, two Egyptian security sources said, and now engaged in intense contacts to salvage the ceasefire and return to talks.
Much of Gaza now lies in ruins after the war, which erupted on October 7, 2023, when Hamas-led gunmen attacked Israeli communities, killing some 1200 people, according to Israeli tallies, and abducting 251 hostages into Gaza.
The Israeli campaign in response has killed more than 48,000 people in Gaza, according to Palestinian health authorities.
with AP
