Palestinian residents said on Saturday that houses and open areas had been hit and three mosques destroyed in Khan Younis in the past hours.
Columns of smoke were rising into the sky, Reuters journalists in the city said.
Almost two months into the fighting, the children, women and men of — Martin Griffiths (@UNReliefChief) #Gaza are all terrified. They have nowhere safe to go and very little to survive on. They live surrounded by disease, destruction and death.My statement on the end of the pause. https://t.co/zT56NnqbLy pic.twitter.com/zZeldeKwmpDecember 1, 2023
The Israeli military said that in the last 24 hours, combined attacks by its ground, air and naval forces had hit 400 militant targets and killed an unspecified number of Hamas fighters.
Hamas media said about 200 Palestinians had been killed since the end of the truce - adding to the more than 15,000 dead in Gaza since the start of the war, according to health authorities in the enclave.
The warring sides blamed each other for the collapse of the seven-day truce, during which Hamas had released hostages in exchange for Palestinian prisoners held in Israeli jails.
The United Nations said the fighting would worsen an extreme humanitarian emergency.
"Hell on earth has returned to Gaza," said Jens Laerke, spokesperson for the United Nations humanitarian office in Geneva.
The conflict broke out on October 7 when Hamas militants crossed into southern Israel and killed 1200 people, mostly civilians, in a rampage against kibbutzim and other communities.
More than 200 hostages were taken back to Gaza.
Israeli forces have hit targets in the Gaza Strip after a week-long truce expired. (AP PHOTO)
Israel responded with a ferocious bombing campaign and a ground offensive which has destroyed large areas of Gaza and displaced hundreds of thousands of people in what has become the the bloodiest episode of the wider Israel-Palestinian conflict.
Friday saw intense bombing in Khan Younis and Rafah in the south, medics and witnesses said.
Displaced Gazans have been sheltering there because of fighting in the north of the densely populated enclave but residents said they feared Israel was preparing for ground troops to move on the south.
Leaflets dropped by Israel on eastern areas of Khan Younis ordered residents of four towns to evacuate - not to other areas in Khan Younis as in the past, but further south to Rafah.
"You have been warned," the leaflets said in Arabic.
Parts of southern Gaza have come under intensive bombardment since the truce collapsed. (EPA PHOTO)
The Israeli military said it had killed many squads of fighters in northern Gaza, including in a gunbattle at a mosque used by Islamic Jihad militants as a command post.
Signalling that it was deepening its grip on the north, it also instructed civilians in several districts of Gaza City to evacuate immediately.
In southern Israel, rocket sirens sounded early on Saturday in communities near the border with Gaza, but there were no reports of serious damage or casualties.
Reuters could not confirm the battlefield accounts.
The truce that started on November 24 had been extended twice but after seven days during which women, children and foreign hostages were freed as well as Palestinian prisoners, mediators failed to find a formula to release more.
Israel accused Hamas of refusing to release all the women it held.
A Palestinian official said the breakdown occurred over female Israeli soldiers.
More than 100 were killed and dozens injured within hours of the fighting resuming in Gaza. (EPA PHOTO)
Qatar, which has played a central mediating role, said negotiations were continuing with Israelis and Palestinians to restore the truce but Israel's renewed bombardment of Gaza had complicated matters.
An Israeli official in Washington said it was a "very high priority" to get as many hostages released as possible.
"And for that, under agreed terms, Israel is willing to give additional pauses," the official said.
"We can negotiate while we still fight."
US Defense Secretary Lloyd Austin blamed Hamas for failing to meet conditions on hostages and for an attack in Jerusalem during the ceasefire.
"We're going to continue to work with Israel and Egypt and Qatar on efforts to re-implement the pause," Austin told a press conference in California.
Hamas accused Washington of giving the green light for an Israeli "war of genocide and ethnic cleansing".
