Hundreds of people are believed to be inside a hospital in northern Gaza that was attacked by Israel's forces.
The Israeli military's operation in the Palestinian enclave continued on Monday.
The military announced that it has detained more than 300 militants, including Hamas fighters, since it began the ground operation in the Gaza Strip. It said they have been taken to Israel for further interrogations.
On Monday, Qatar-based Al Jazeera TV station broadcast a video that showed the inside of Gaza's Indonesian Hospital. The facility was hit by Israeli strikes on Sunday.
Badly damaged ceilings can be seen in the footage. The report said 12 people, including patients, were killed in the hospital by the assault. It added that about 700 people are still inside the compound, which has been surrounded by Israeli troops.
An Indonesian humanitarian aid group that provides support for the hospital held a news conference in Jakarta. It urged Israel to stop the attacks.
The head of the World Health Organization, Tedros Adhanom Ghebreyesus, issued a social media post. He said, "Health workers and civilians should never have to be exposed to such horror, and especially while inside a hospital."
Al Jazeera has also reported that Israeli strikes hit a UN-operated school at the Bureij refugee camp in central Gaza. It said at least 10 people, including those who were taking shelter there, were killed.
Reuters news agency said on Monday that 40 trucks containing medical equipment, as well as about 180 doctors, nurses and administrators, had entered Gaza through the Rafah crossing on the border with Egypt. Jordan's government has coordinated the delivery of supplies.
The move is part of a plan to set up a field hospital in Khan Younis within 48 hours. Many displaced people are taking shelter in the southern Gaza city.
Observers say measures to improve the ever-deteriorating humanitarian situation in Gaza are urgently needed.