UN Secretary-General Antonio Guterres on Saturday said he was "horrified" by the reported attack in the Gaza Strip on an ambulance convoy outside Al-Shifa hospital.
"The images of bodies strewn on the street outside the hospital are harrowing," Guterres said on Twitter.
"Now, for nearly one month, civilians in Gaza, including children and women, have been besieged, denied aid, killed, and bombed out of their homes," he noted, adding simply: "This must stop."
Guterres called on Hamas to "immediately and unconditionally" release all hostages held in Gaza.
Underlining that the humanitarian situation in Gaza is "horrific," Guterres reiterated his call for a humanitarian cease-fire.
"International humanitarian law must be respected. Civilians and civilian infrastructure, including humanitarian and medical workers and assets must be protected. Civilians must also not be used as human shields," he said.
The Israeli army on Friday targeted the main gate of Al-Shifa Hospital in Gaza City, according to an Anadolu correspondent at the scene.
The Israeli military said it hit ambulances, meters away from the Al-Shifa Hospital, claiming that it was used by Palestinian group Hamas. Hamas has denied the claims.
At least 13 people were killed and 26 others injured by Israeli bombing targeting ambulances in front of the hospital, according to the Health Ministry in Gaza.
The strikes on or near hospitals joined a number of Israeli army attacks in recent weeks damaging or destroying civilian buildings, attacks which apparently violate the rules of war and have drawn international outrage.
This week the Israeli army expanded its air and ground attacks on the Gaza Strip, which has been under relentless airstrikes since a surprise offensive by Hamas on Oct. 7.
Nearly 11,000 people have been killed in the conflict, including 9,488 Palestinians and more than 1,538 Israelis.