The Gaza Health Ministry claimed Tuesday evening that at least 500 people were killed in an Israeli airstrike at a hospital in Gaza City where scores of people were seeking shelter.

Just a couple hours later, Israeli military officials denied any involvement in the explosion, instead blaming the blast at the Anglican-run al-Ahli Hospital on a misfired Palestinian rocket.

“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,” the Israeli military said in a statement. “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.”

Hundreds of people, including women and children, were taking shelter at the hospital, which is run by the Episcopal Diocese of Jerusalem, during the explosion at around 7 p.m. local time, according to Palestinian officials. Footage and photos from the fiery scene showed shattered glass and body parts scattered across the rubble of hospital hallways and rooms. Many of the victims in the devastating images appeared to be young children.

Just a few days earlier, Israeli rocket fire had destroyed two floors of the hospital’s cancer center, injuring four staffers. The hospital was one of several Gaza buildings reduced to rubble on Tuesday. Dozens of civilians and at least one senior Hamas official were killed in strikes by Israel, which military officials said were aimed at Hamas targets.

In the wake of the hospital blast, the Palestinian Civil Defense blamed Israel for what it called an “unprecedented” attack on innocent lives that amounts to genocide.

“The massacre at al-Ahli Arab Hospital is unprecedented in our history,” spokesman Mahmoud Basal told Al Jazeera. “While we’ve witnessed tragedies in past wars and days, what took place tonight is tantamount to a genocide.”

Anadolu Agency via Getty Images

Dr. Zeena Salman, an American pediatric oncologist who once volunteered in Gaza for eight years, described the strike as “vile, horrific, and beyond my comprehension” in an interview with The Daily Beast.

“Everybody knows at this point that these hospitals are full of sick patients and families seeking refuge, trying to find some tiny sliver of safety,” said Salman, who is based in the U.S. but remains in contact with colleagues in Gaza. “Oct. 17 is probably going to go down as a day that goes down in history as one of the most atrocious war crimes we have ever seen.”

The Palestinian Authority President Mahmoud Abbas declared three days of mourning and called on Palestinians in the West Bank to observe a commercial strike on Wednesday. The leader said he would be returning to the West Bank from Jordan, calling off a scheduled meeting with President Joe Biden on Wednesday in protest. Later that night, Jordanian authorities announced they’d no longer host Biden for a summit, which was also set to include Jordan’s King Abdullah and the Egyptian president, Abdel Fatah al-Sisi.

Ziad Shehadah, a doctor in Gaza, told Al Jazeera that the hospital was filled with civilians seeking a safe place amid a seemingly endless barrage of airstrikes from Israel.

“People left their homes thinking they were more dangerous and they move to our schools and hospitals to be safe,” he said. “And in one minute, all of them have been killed at a hospital.”

Shehadah called the attack a “massacre,” projecting that casualty numbers will eventually eclipse 1,000 people.

Anadolu Agency via Getty Images

Most of those injured in the blast were transported to al-Shifa hospital, The Washington Post reported. A doctor there told the paper that they’ve become so overwhelmed with the number of injured and dead that bodies are being ditched in hallways.

Nebal Farsakh, a representative from the Palestinian Red Crescent Society, told Al Jazeera that many of those killed in the blast were Palestinians who attempted to heed Israel’s evacuation orders but couldn’t escape further south because of Gaza City’s devastated infrastructure.

He said the hospital was one of the few “safe spaces” remaining for families. The hospital was so packed, some refugees were forced to stay outside the hospital’s doors, he said.

“They are forced to evacuate themselves under continuous bombardment,” he said. “The only available is a hospital, so they’re thinking that they would be in a safe place. This is genocide. This is a war crime.”

In a tweet, Israel Prime Minister Benjamin Netanyahu blamed the blast on “barbaric terrorists” in Gaza.

“The entire world should know: It was barbaric terrorists in Gaza that attacked the hospital in Gaza, and not the IDF,” he posted. “Those who brutally murdered our children also murder their own children.”

Daoud Shehab, a spokesman for Islamic Jihad, denied Netanyahu’s claim in a statement to The New York Times—saying the group hasn’t been conducting any military operations near the hospital.

“There were no operations by the Al-Quds Brigades in the area at all,” Shehab told the Times by phone, referring to the group’s armed wing.

Reuters/Mohammed Al-Masri

Top U.S. officials have appeared reluctant to say much in the blast’s immediate aftermath. Sabrina Singh, a Defense Department spokesperson, said U.S. officials have repeatedly warned Israel’s defense minister, Yoav Gallant, to avoid killing civilians and to obey the laws of war.

Singh conceded that she “does not have all of the facts,” but said the U.S.’ backing of Israel’s war against Hamas “does not mean the innocent killing of civilians.”

President Joe Biden did not immediately make a statement on the incident. Other world leaders were quick to condemn the attack, however, including Canadian Prime Minister Justin Trudeau.

“The news coming out of Gaza is horrific and absolutely unacceptable,” he told reporters Tuesday. “International law needs to be respected in this and in all cases. There are rules around wars and it’s not acceptable to hit a hospital.”

Turkey’s foreign ministry called it a “barbaric attack,” saying in a statement that they condemn the strike in the “strongest terms.” Iran’s foreign ministry issued a similarly worded statement, calling the attack a “savage war crime” that killed hundreds of “unarmed and defenseless people.”

The future of the hospital, which has long provided essential services to Palestinians, remains uncertain. It’s owned and operated by the Episcopal Diocese of Jerusalem, and the head of its American fundraising division, Eileen Spencer, told the Post the structure may be totally unusable.

“We don’t know if the hospital will still be standing,” she said.