About 500 Palestinians have been killed in a blast at a Gaza hospital that Palestinian health authorities say was caused by an Israeli air strike but 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, which rules the Gaza Strip.

Arab countries, Iran and Turkey swiftly condemned the attack. The Palestinian prime minister called it “a horrific crime, genocide” and said countries backing Israel also bore responsibility.

Hamas said the bombing mostly killed people left homeless by Israel bombardments, and that the dead included patients, women and children.

“There are scores of dismembered and crushed bodies, baths of blood,” said Izzat El-Reshiq, a senior Hamas member.

Video obtained by Reuters showed several full ambulances arriving at another Gaza hospital carrying people injured at Al-Ahli al-Arabi hospital. One man was staggering, bleeding heavily from the head. A boy was being carried on a stretcher.

Israel’s military denied responsibility for the attack, saying military intelligence suggested the hospital was hit by a failed rocket launch by the enclave’s Palestinian Islamic Jihad militant 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 representative for the Israel Defence Forces said in a statement.

In Washington, the Pentagon said it was aware of the reports about the hospital being hit but had no details. The Pentagon, which has sent five C-17 aircraft with military assistance to Israel so far, reiterated that there were no preconditions on the aid being provided and added: “We expect all democracies like Israel to uphold the law of war.”

Israel has vowed to annihilate the Hamas movement that controls Gaza after Hamas gunmen killed 1300 people, mainly civilians, during a rampage through southern Israeli towns on October 7 – the deadliest single day in Israel’s 75-year history.

Israel has imposed a total blockade on Gaza, halting food, fuel and medical supplies, which are rapidly running out.

Scores of trucks carrying vital supplies for Gaza headed towards the Rafah crossing in Egypt on Tuesday, the only access point to the coastal enclave outside Israel’s control, but there was no clear indication that they would be able to enter.

Earlier on Tuesday, German Chancellor Olaf Scholz arrived in Israel to show solidarity with the country following attacks from Hamas.

Scholz said on Tuesday that “Germany stands firmly by Israel’s side,” in a post on X.

The German chancellor is the second head of government to visit the country since the Hamas attack 10 days ago, after Romanian Prime Minister Marcel Ciolacu arrived in Israel earlier on Tuesday.

US Secretary of State Antony Blinken announced Biden’s planned visit at the end of hours of talks with Netanyahu, in which he said Netanyahu had agreed to develop a plan to get humanitarian aid to Gaza civilians. 

He gave no details.

Biden will “hear from Israel what it needs to defend its people” when he visits on Wednesday, Blinken said. 

He will also hear how Israel will carry out operations in a way that minimises civilian casualties and lets humanitarian aid into Gaza to help civilians “in a way that does not benefit Hamas”.

The United Nations agency for Palestinian refugees, UNRWA, said only about 14 per cent of Gazans had access to water through a single pipe to Khan Younis that Israel allowed to open for three hours on Monday.

Concerns about dehydration and diseases were high as water and sanitation services had collapsed.

“People will start dying without water,” UNRWA said.

Israel says 199 hostages were taken to Gaza during the militants’ raid. 

Hamas released a video of one French-Israeli hostage, Maya Schem, calling on world leaders to help her and other captives get home.