An airstrike by a U.S.-backed, Saudi-led coalition killed more than 100 people and injured hundreds more at a funeral Saturday, according to Health Ministry officials and medical groups. With the death toll expected to rise, it was one of the deadliest single assaults in the 20-month-old civil conflict that has fractured the Middle East’s poorest country.

Witnesses said at least three airstrikes hit the Grand Hall, one of the biggest arenas in the Yemeni capital, Sanaa, as mourners gathered inside to attend a funeral for the father of a top rebel Houthi official. In attendance were senior political and military officials aligned with the Houthis and hundreds of civilians, according to witnesses.

As explosions rocked the hall at around 3:30 p.m., chaos ensued as people tried to rush toward the exits. Many jumped through a large opening in a wall that had crumbled, said Mohammed Ahmed al-Sunaidar, an Interior Ministry employee. He was just arriving at the hall and ran inside to help survivors.

“We carried many bodies,” Sunaidar said. “But we couldn’t carry the bodies that were completely burned. There were body parts scattered all over the place.”

Most of those who died, he added, were in the hall’s left wing, which was struck by one of the missiles.

A Yemeni collects items amid the rubble of a destroyed building following reported airstrikes by Saudi-led coalition airplanes on the capital Sanaa on Saturday, Oct. 8, 2016. (Mohammed Huwais/AFP/Getty Images)

Tameem al-Shami, a Health Ministry spokesman, said 104 people were killed and more than 550 were injured, many of them critically. Some news reports said the death toll had reached at least 155.

The Saudi-owned Al Arabiya satellite network, citing Saudi military sources, said the coalition did not stage the airstrike on the hall. But Saudi Arabia’s military have previously denied strikes on hospitals and other civilian areas that were later proved to have occurred.

The United Nations on Saturday “unequivocally condemned” the attack, adding that the death toll was 140, with more than 525 injured. It called for an investigation, saying it was “shocked and outraged by today’s airstrikes,” according to a statement by Jamie McGoldrick, U.N. humanitarian coordinator in Yemen.

A White House National Security Council spokesman announced in a statement that the United States would initiate an immediate review of “our already significant reduced support” to the Saudi-led forces.

“We are deeply disturbed by reports of today’s airstrike on a funeral hall in Yemen, which, if confirmed, would continue the troubling series of attacks striking Yemeni civilians,” said council spokesman Ned Price. “U.S. security cooperation with Saudi Arabia is not a blank check.”

The medical charity Doctors Without Borders reported that more than 400 people injured by the airstrikes were receiving treatment at six hospitals they are affiliated with in the capital. Health Ministry officials called on citizens to donate blood and urged all off-duty doctors to leave their homes and help treat the injured in the hospitals.

“There are still many bodies that are at the scene until this moment,” Sunaidar said. “That’s because the bodies are completely burned and cannot be identified.”

The funeral was being held for the father of Interior Minister Galal al-Rowaishan, who was appointed by the Houthi-led administration and is a key ally of former Yemeni president Ali Abdullah Saleh. The former president was ousted in the aftermath of Yemen’s populist revolt, part of the Arab Spring uprisings of five years ago but later aligned himself with the Houthis and remains powerful.

Yemen’s conflict pits an alliance between the Shiite Houthi rebels and Saleh’s loyalists against President Abed Rabbo Mansour Hadi, who is backed by Saudi Arabia, the United States and their allies. In February 2015, the Houthis seized Sanaa and forced Hadi southwardto the port city of Aden. That prompted Saudi Arabia to enter the war and attempt to restore Hadi to power. The Sunni Muslim monarchy has long been concerned about the Houthis and their links to its main regional rival, Iran’s Shiite theocracy.

As many as 10,000 people, mostly civilians, have been killed, according to the United Nations. Millions more are suffering from hunger, illness and displacement as the nation is in the throes of a humanitarian disaster .

Human rights groups have accused the Saudi-led coalition of human rights violations, which Riyadh has denied. The Houthis also have been accused of abuses, such as recruiting child soldiers and forced disappearances of its opponents.

The Obama administration is facing growing criticism for supporting Saudi Arabia’s air campaign. Some lawmakers and human rights groups are charging that the United States bears some responsibility for the mounting casualties.

Raghavan reported from Cairo. Karen DeYoung contributed to this report.