Israeli forces have been conducting airstrikes on a heavily populated area in the Gaza Strip, with attacks on hospitals leaving many casualties.

Health authorities in Gaza say Israeli bombardments in the northern region of Jabalia on Sunday killed 100 people, wounded 20 and left some 100 others trapped under rubble.

They also say Israeli shelling in the southern Gaza city of Khan Younis killed a 13-year-old girl being treated at Nasser Hospital. She reportedly had lost her parents and siblings, as well as one of her legs, from a previous Israeli airstrike.

A large number of casualties have been also reported at Al-Shifa Hospital in Gaza City.

Other reports say bodies were found under the rubble of Kamal Adwan Hospital in northern Gaza after Israeli troops destroyed it with bulldozers.

Local health authorities are calling for an international investigation.

WHO Director-General Tedros Adhanom Ghebreyesus wrote on social media that the WHO "is appalled" by the destruction, which he said rendered the hospital non-functional and resulted "in the death of at least 8 patients."

US Defense Secretary Lloyd Austin is on a tour of the Middle East.

He is scheduled to visit Israel on Monday to meet Prime Minister Benjamin Netanyahu and Defense Minister Yoav Gallant. They are expected to discuss the possibility of scaling back combat operations in the Gaza Strip.

The United States is calling for Israel to quickly transition to a more limited, focused campaign to curb the number of civilian casualties.