Antonio Guterres, secretary-general of the United Nations, has said he condemns the blast at al Ahli hospital, which officials say killed at least 500 people.
He said he was “horrified” by the incident and said his heart is with the families of the victims.
It comes as Israel and Palestinian officials have traded blame over who was responsible.
Within the last hour, the Israel Defence Forces (IDF) claimed it had confirmed the hospital was hit by a rocket launched by Islamic Jihad.
Meanwhile, the leader of Hamas has said that the US “holds the responsibility of the hospital attack because of the cover it gives to Israeli aggression”.