Israel launched dozens of airstrikes across the Gaza Strip after a temporary truce with Hamas expired on Friday morning.
At least six people have died in the raids and dozens have been injured so far, the Palestinian health ministry said.
Palestinian media reported Israeli air and artillery strikes across the enclave after the truce expired, including in Rafah, near the border with Egypt.
The Israel military confirmed its jets were striking Hamas targets in Gaza.
Images on social media showed large plumes of dark smoke rising over the densely built-up Jabalia camp in Gaza.
Areas near the Nasser Hospital in Khan Younis, south of the Gaza Strip, and a home in Gaza City were also hit in the raids, an Al Arabiya correspondent said.
The bombings also targeted the Abasan town in Khan Yunis, Al Arabiya reported, citing Palestinian media sources.
Hundreds of thousands of Palestinians have sought shelter in the south in areas Israel deemed as safe zones. During the truce, the Israeli military had also prevented Gazans from returning to their homes in the northern part of the enclave.
The heavy fighting reported in Gaza came as Israel’s military said it had resumed combat operations against Hamas after accusing the Palestinian militant group of violating the truce by firing towards Israeli territory.
The seven-day pause, which began on Nov. 24 and was extended twice, had allowed for the exchange of dozens of hostages held in Gaza for hundreds of Palestinian prisoners and facilitated the entry of humanitarian aid into the shattered coastal strip.
In the hour before the truce was set to end at 7 a.m. (0500 GMT), Israel said it intercepted a rocket fired from Gaza.
Further sirens warning of rockets sounded again in Israeli areas near Gaza just minutes before the deadline, the military said.
There was no immediate comment from Hamas or claim of responsibility for the launches.
Israel has sworn to annihilate Hamas, which rules Gaza, in response to the Oct. 7 incursion by the militant group, when Israel says gunmen killed 1,200 and took 240 hostages.
Israel retaliated with intense bombardment and a ground invasion that has killed more than 15,000 people, including thousands of children.
Blinken calls for safe zones
US Secretary of State Antony Blinken had on Thursday urged Israel to create safe zones for Palestinian civilians in Gaza before it resumes “major military operations” in the Hamas-ruled territory.
Israel “must put in place humanitarian civilian protection plans that minimize further casualties of innocent Palestinians,” he told reporters in Tel Aviv, “including by clearly and precisely designating areas and places in southern and central Gaza, where they can be safe and out of the line of fire.”
He said protecting civilians meant avoiding further “significant displacement of civilians inside Gaza” as well as “damage to life (or) critical infrastructure like hospitals, like power stations, like water facilities.”
“And it means giving civilians who have been displaced in southern Gaza the choice to return to the north as soon as conditions permit.”
There should be no “enduring internal displacement,” he said.
Qatar’s mediation success: Behind-the-scenes of brokering Israel-Hamas truceAs world leaders feted Qatar for brokering a truce between Israel and Hamas last ... Middle East
Hamas ‘willing to extend truce’ with Israel: Source close to groupHamas is “willing to extend the truce” in fighting with Israel, a source close to ... Middle East
‘We want an eighth day and beyond,’ says Blinken on Gaza truce extensionUS Secretary of State Antony Blinken called Thursday for a further extension to a ... Middle East