GAZA – About 500 Palestinians were killed in a blast at a Gaza hospital on Tuesday that Palestinian health authorities said was caused by an Israeli air strike but that the Israeli military blamed on a failed rocket launch by a Palestinian militant group.

The blast was the bloodiest single incident in Gaza since Israel launched an unrelenting bombing campaign against the densely populated territory in retaliation for a deadly cross-border Hamas assault on southern Israeli communities on October 7.

It took place on the eve of a visit by US President Joe Biden to Israel to show support for the country in its war with Hamas, the Islamist group that rules the Gaza Strip, and to hear how Israel plans to minimize civilian casualties.

Reuters could not independently verify who was responsible for the blast.

The health minister in the Hamas-run government of Gaza, Mai Alkaila, accused Israel of a massacre. A Gaza civil defence chief said 300 people were killed and a health ministry official said 500 were killed.

However, the Israeli military denied responsibility for the blast at the Al-Ahli al-Arabi hospital in Gaza City, suggesting the hospital was hit by a failed rocket launch by the enclave’s Palestinian Islamic Jihad military group.

“An analysis of IDF operational systems indicates that a barrage of rockets was fired by terrorists in Gaza, passing in close proximity to the Al Ahli hospital in Gaza at the time it was hit,” a spokesperson for the Israel Defense Forces said.

“Intelligence from multiple sources we have in our hands indicates that Islamic Jihad is responsible for the failed rocket launch which hit the hospital in Gaza,” the spokesperson added.

Daoud Shehab, a spokesman for Islamic Jihad, told Reuters: “This is a lie and fabrication, it is completely incorrect. The occupation is trying to cover for the horrifying crime and massacre they committed against civilians.”

In the occupied West Bank city of Ramallah, Palestinian security forces fired tear gas and stun grenades to disperse protesters throwing rocks and chanting against President Mahmoud Abbas as popular anger boiled over after the blast.

Clashes with Palestinian security forces broke out in a number of other cities in the West Bank, which is ruled by Abbas’ Palestinian Authority, late on Tuesday, witnesses said.