Gaza's civil defence said Sunday health workers had uncovered at least 180 bodies of people killed and buried by Israeli forces at the Nasser Hospital in the southern city of Khan Younis.
Israeli tanks and armoured vehicles had surrounded the medical complex on March 26.
Hamas condemned what it said was a "mass grave of those executed in cold blood and buried with military bulldozers in the hospital's courtyard".
Overnight Israeli strikes on the the city of Rafah in the southern Gaza Strip killed 22 people, including 18 children, health officials said Sunday, as the United States approved a massive aid package worth billions of dollars in military aid to Israel.
Israel's war on the Gaza Strip has killed over 34,000 Palestinians, according to the health ministry, and left the territory in ruins. Around 80% of the population have fled their homes to other parts of the besieged coastal enclave, which is on the brink of famine .