Hundreds of people were feared dead after an explosion at a hospital in the Gaza Strip on Tuesday, a little over a week after the Palestinian group Hamas staged a terrorist attack on Israel that killed 1,400 people and led Israel to declare war and begin bombing the territory.

Hamas, which controls Gaza, blamed the blast on an Israeli airstrike. Israel said it was caused by an errant rocket fired by another armed group, Palestinian Islamic Jihad, which denied the assertion.

On Wednesday, President Joe Biden backed Israel’s position, citing “the data I was shown by my Defense Department.”

The competing claims have not been independently verified. The New York Times is working to assess the various accounts through an analysis of photos, video footage and other evidence, as well as on-the-ground interviews.

Here is what we know so far about the explosion at the Ahli Arab Hospital in Gaza City.

What do we know about the death toll?

On the night of the explosion, a spokesperson for the Gazan health ministry put the toll at 500 or more dead, which the ministry later changed to “hundreds.” No figure could be confirmed independently, but images from the hospital and witness accounts made clear that it was high.

Mohammad Abu Selim, head of the nearby Shifa Hospital, said in an interview hours after the blast that 150 to 200 people killed in the explosion were taken to his hospital, along with about 300 people who had been wounded. He said he had no official tally of the dead because of the terrible condition of many of the bodies.

The Israeli military said Wednesday morning that the number of casualties was inflated. The Gazan health ministry, which is run by Hamas, said later Wednesday that 471 people had been killed and hundreds more injured.

The figures could not be independently confirmed, although video footage verified by The New York Times shows scores of bodies strewn across the hospital’s courtyard.

The hospital is run by the Anglican Church and overseen by Archbishop Hosam Naoum, who said that in recent days, large numbers of people had taken shelter there to escape Israeli airstrikes. The hospital usually has 80 beds, according to the diocese website.

What did the United States government say?

Adrienne Watson, a spokesperson for the National Security Council, said Wednesday that the U.S. government “assesses that Israel was not responsible for an explosion that killed hundreds of civilians yesterday at the Al Ahli Hospital in the Gaza Strip.”

“Our assessment is based on available reporting, including intelligence, missile activity and open-source video and images of the incident,” she said, adding that the United States was continuing to collect information.

Watson said the intelligence indicated that some Palestinian fighters in the Gaza Strip believed the explosion had likely been caused by an errant rocket or missile launch carried out by Palestinian Islamic Jihad. “The militants were still investigating what had happened. We continue to work to corroborate whether the explosion resulted from a failed PIJ rocket,” she said.

U.S. officials, speaking on the condition of anonymity to discuss sensitive information, said that multiple strands of early intelligence, including infrared satellite data, show a launch of a rocket or missile from Palestinian fighter positions within Gaza. They cautioned that the analysis was preliminary.

A senior Defense Department official said that, based on data collected by infrared sensors, the United States was “fairly confident” the launch did not come from Israeli forces.

What did Palestinian Islamic Jihad say?

Palestinian Islamic Jihad, whose members participated in the Hamas-led attacks on Israel on Oct. 7, denied that an errant rocket from its arsenal had caused the explosion.

In a phone interview with the Times on Wednesday, a spokesperson for the group, Musab Al-Breim, said that the capacity of their weapons supply was “primitive.”

In a statement Tuesday, the group said video footage and the extent of the destruction showed that the blast was caused by an Israeli aerial bombardment.

The group’s military wing posted a message on Telegram at 7:09 p.m. on the night of the explosion saying it had fired a barrage of rockets toward Israel — just minutes after the blast occurred. But Al-Breim said the timing of posts did not always indicate the timing of launches.

He acknowledged that errant rockets from the military wing had killed Palestinians in the past. “We have made mistakes, I am not going to deny it,” he said. “However, not mistakes of this size.”

What did the Israeli army say?

Citing aerial footage, photos taken in the aftermath of the explosion and recordings it said were of Hamas members, the Israeli military said Wednesday that the blast was caused by a rocket that misfired after being launched by Palestinian Islamic Jihad.

Rear Adm. Daniel Hagari, the chief spokesperson for the Israeli military, said the Palestinian group fired 10 rockets at 6:59 p.m. on the night of the explosion, and that one of them fell to earth prematurely, hitting a parking lot outside the hospital. He denied that Israel had fired any ordnance in the area of the hospital at that time.

He cited a photo of the parking lot that was posted on social media Wednesday morning that he said did not show the kind of impact that would have been caused by an Israeli missile. The photo shows the effects of a fire — burned-out cars and scorched ground — that he said was caused by rocket fuel.

He also showed an aerial image that he said was taken from a military drone overnight. In the image, he said, there was no evidence of a crater that would have been caused by an Israeli missile.

Hagari dismissed suggestions that the strike was caused by an errant Israeli air defense interceptor; he said Israel does not fire air defense missiles into Gazan airspace.

The admiral played a recording of what he said was a wiretapped conversation between two Hamas members, in which one speaker says the damage was caused by a rocket fired by Palestinian Islamic Jihad from a cemetery near the hospital. The Times is assessing the material and has not verified the conversation.

What did Hamas say?

In a statement, Hamas said the explosion was “a horrific massacre” and “a crime of genocide” caused by an Israeli airstrike.

The Ahli Arab Hospital had been hit previously by rocket fire on Saturday, according to the Gazan health ministry and video footage verified by the Times. The Anglican Church said in a statement that four staff members were injured in that blast.

Yousef Abu al-Rish, the top official for the Gazan health ministry, said at a news conference Tuesday night that the Israeli military had called the hospital director and told him that the earlier blast had been a warning to evacuate.

On Wednesday, Naoum said that the Israeli military had called and texted the hospital managers at least three times in recent days, asking its patients and staff to leave the hospital compound. He said the warnings were particular to the hospital, and not part of Israel’s wider push to encourage civilians to leave northern Gaza for the territory’s south.

“There were specific warnings to get out of the building,” the archbishop said.

Lt. Col. Amnon Shefler, an Israeli military spokesperson, said the calls to the hospital were part of a wider campaign to urge civilians to leave northern Gaza ahead of an expected Israeli invasion. Shefler said the hospital was not a target for the military.

The New York Times New Service