Israel's military chief has revealed that his country's forces have begun ground operations in the southern Gaza Strip.

Israel Defense Forces Chief of the General Staff Herzi Halevi said on Sunday that Israeli troops started operations against Hamas in southern Gaza the day before.

He said that just as soldiers fought strongly and thoroughly in northern Gaza, they are also doing so in the south.

Hamas is apparently fighting back, as there have been reports of intense combat several kilometers north of the major southern city of Khan Younis.

Israel resumed its military operations in Gaza on Friday, saying it aims to bring back the remaining hostages held by Hamas and eliminate the Islamic group.

On Sunday, Israel continued bombardment all over Gaza.

It carried out an airstrike on the Jabalia refugee camp in northern Gaza for the second consecutive day. Qatar-based satellite TV station Al Jazeera reported the attack killed more than 100 people. Footage of the site shows children searching through the rubble for their families and a boy screaming out that his father and brother have been killed.

Israeli forces also conducted intense bombardment on Khan Younis. Israel's military said it distributed leaflets ahead of the strike telling residents to move further south. But many injured people were seen carried to local hospitals.

Health authorities in Gaza say that over the past three days they confirmed 316 deaths and 664 injuries. They say the actual figures are much higher.

The authorities also say 15,523 people have died and 41,316 others have been wounded over nearly two months since the start of the fighting.

A spokesperson for the authorities says many died from the loss of blood amid shortages of medical supplies and medical workers.

A UNICEF official working in Gaza warns that there are growing risks of children becoming victims of the fighting or infectious diseases amid the worsening hygiene situation.