Israeli Prime Minister Benjamin Netanyahu said he had instructed the military to take "strong action" against the Palestinian Islamist group Hamas in Gaza in response to the group's refusal to release hostages held there and rejection of ceasefire proposals.
"Israel will, from now on, act against Hamas with increasing military strength," the prime minister's office said on Tuesday.
After heavy strikes, the Israeli army issued evacuation orders for a number of neighbourhoods in Gaza, according to a statement.
Hamas, meanwhile, accused Israel of overturning the hard-fought ceasefire deal, leaving the fate of 59 hostages still held in Gaza uncertain.
Israel's renewed 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.
US President Donald Trump said on Monday he would hold Iran responsible for any further attacks on international shipping carried out by the Houthi group, as his administration expanded strikes in Yemen.
Strikes in Gaza were reported in multiple locations. Palestinian health ministry officials said many of the dead were children.
The Israeli military said it hit dozens of targets and the attacks would continue for as long as necessary and extend beyond air strikes, raising the prospect that Israeli ground troops could resume fighting.
The attacks were far wider in scale than the regular drone strikes Israel has said it has conducted recently against individuals or small groups of suspected militants, and follows weeks of failed efforts to agree an extension to the truce agreed on January 19.
Israel has weakened Hamas and the group's Lebanese ally Hezbollah, killing their leaders while launching attacks on the Houthis, all members of what has been called Iran's "Axis of Resistance" against US and Israeli interests.
Among those killed was Mohammad Al-Jmasi, a senior member of Hamas' political office, and members of his family, including his grandchildren who were in his house in Gaza City when it was hit by an air strike, Hamas sources and relatives said.
In all, at least five senior Hamas officials were killed along with members of their families.
The Gaza health ministry said the death toll had risen to 326, with authorities also reporting separately that 16 members of one family in Rafah, in southern Gaza, had been killed.
In Washington, a White House spokesperson said Israel had consulted the US administration before it carried out the strikes.
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, which saw 33 Israeli hostages and five Thais returned by militant groups in Gaza 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 to halt fighting 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 from Gaza, in accordance with the terms of the original ceasefire agreement.
Each side has accused the other of failing to respect the terms of the January ceasefire agreement, but until now, a full return to the fighting had been avoided.
Much of Gaza now lies in ruins after 15 months of fighting, which erupted on October 7, 2023, when thousands of Hamas-led gunmen attacked Israeli communities around the enclave, 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, according to Palestinian health authorities.
with AP
