Israel's Prime Minister Benjamin Netanyahu has vowed to keep fighting against Hamas until his country achieves its goals of destroying the militant group and freeing all hostages it holds.
Mr Netanyahu ordered the resumption of air strikes across Gaza early on Tuesday, local time, saying the attack was "only the beginning".
The strikes killed more than 400 people, mostly women and children, according to the Hamas-run Gaza Health Ministry.
"Hamas is responsible for this war," Mr Netanyahu said during his speech.
"It invaded our towns, murdered our people, raped our women and kidnapped our loved ones.
"Hamas refused offer after offer to release our hostages.
"This is why I authorised yesterday the renewal of military action against Hamas."
The war erupted after Hamas-led gunmen attacked Israel, killing some 1,200 people, according to Israeli tallies.
The Israeli campaign in Gaza has killed more than 48,000 people, say Hamas-run health authorities.
The Israeli strikes during the Muslim holy month of Ramadan come after the Islamist group refused to release more of the 59 hostages it holds in Gaza.
Mr Netanyahu also urged people in Gaza to move to safer areas to stay out of harm's way.
"Palestinian civilians should avoid any contact with Hamas terrorists," the Israeli prime minister warned.
"When these terrorists embed themselves in civilian areas, when they use civilians as human shields, they're the ones who are responsible for all unintended casualties."
All further ceasefire negotiations will take place "under fire", he added.
The escalation of the Israel-Hamas war has prompted great concerns, with protesters gathering in Tel Aviv to oppose Mr Netanyahu's decision to launch air strikes on Gaza.
The return of fighting in Gaza could jeopardise the Israeli hostages who are still held there — 24 of whom are believed to be still alive.
The Israeli military ordered people to evacuate eastern Gaza and head toward the centre of the territory, indicating that Israel could soon launch renewed ground operations, according to the Associated Press (AP).
The new campaign comes as aid groups warn supplies are running out two weeks after Israel cut off all food, medicine, fuel and other goods to Gaza's 2 million Palestinians.
America backs air strikes
The US said it had been consulted and voiced support for Israel's actions.
The White House said Washington would back Israel in its next steps.
The renewal of the campaign against Hamas, which receives support from Iran, came as the US and Israel stepped up attacks this week across the region.
A senior Hamas official said Israel's decision to return to war amounted to a "death sentence" for the remaining hostages.
Izzat al-Risheq accused Mr Netanyahu of launching the strikes to save his far-right governing coalition.
Hamas said at least six senior officials were killed in Tuesday's strikes. Israel said they included the head of Hamas's civilian government, a justice ministry official and two security agency chiefs.
There were no reports of any attacks by Hamas several hours after the bombardment.
Concerns from European and Middle Eastern leaders
European and Middle Eastern governments expressed concerns the escalation could undermine efforts to end the conflict.
"We want to see this ceasefire agreement re-established as soon as possible," said UK Prime Minister Keir Starmer's spokesman, adding that the reported civilian casualties were "appalling".
In a statement, the French government called for "an immediate end to hostilities" and condemned Tuesday's Israeli strikes on the Gaza Strip.
Italian Prime Minister Giorgia Meloni said the new strikes risked diplomatic efforts to return hostages to Israel.
"We are following with great concern the resumption of fighting in Gaza," she told the Italian Senate.
Qatari Prime Minister Sheikh Mohammed bin Abdulrahman Al Thani called for countries to come together to compel Israel to implement an immediate ceasefire.
Egypt described the strikes as part of "deliberate efforts to make the Gaza Strip uninhabitable and force the Palestinians into displacement".
ABC/AP
