CAIRO — An airstrike, most likely by the Saudi-led coalition, hit near a rural hospital in northern Yemen, killing eight people including five children, according to the charity Save the Children, which supports the facility.

Tuesday’s attack was the latest of many on nonmilitary targets that have killed thousands of civilians in the Middle East’s poorest nation. It came on the fourth anniversary of the Saudi-led coalition’s entry into Yemen’s civil war to support the internationally recognized government against northern rebels known as Houthis.

The Saudi-led coalition, which is backed by the United States, is the only party in the conflict using warplanes, mostly American- and British-made fighter jets.

“We are shocked and appalled by this outrageous attack,” Carolyn Miles, head of Save the Children, said in a statement. “Innocent children and health workers have lost their lives in what appears to been an indiscriminate attack on a hospital in a densely populated civilian area.”

The morning airstrike hit a gas station less than 50 yards from the entrance to Kitaf hospital, according to the charity. The facility, about 60 miles from the northwestern city of Saada, one of the main strongholds of the Houthis, had been open for only a half-hour. Patients and staff were just arriving, said the charity.

Those killed included a health worker who died along with her two children, said the charity. Three other children and a security guard were also killed, as well as one other person. The children ranged in age from 8 to 14.

Two adults are still unaccounted for, suggesting the death toll could rise. An additional seven people were wounded, said the charity, which demanded an immediate investigation into the deaths.

[Yemen’s hunger crisis is from the deliberate policies of the Saudi-led coalition]

“Attacks like these are a breach of international law,” Miles said. “These children have the right to be safe in their hospitals, schools and homes. But time after time, we see a complete disregard by all warring parties in Yemen for the basic rules of war.”

On Wednesday, the coalition took the unusual step of announcing that its own Joint Incidents Assessment Team would investigate the attack to determine whether it was “an unintentional accident,” according to the Saudi Press Agency.

The attack came two days after the release of a Save the Children report that found that at least 226 Yemeni children have been killed and 217 injured in airstrikes by the Saudi-led coalition in the past year — a rate of 37 children harmed per month.

The assault also came a day after the United Nations signed a memorandum of understanding with the coalition in the Saudi capital, Riyadh, that pledged to enhance the protection of boys and girls trapped in Yemen’s war.

According to numbers released this week by the Yemen Data Project, an independent monitoring group, the Saudi-led coalition’s bombing campaign has caused 17,729 civilian deaths and injuries in the past four years of war. These include 3,046 women and children. A quarter of all civilians killed in airstrikes have been women and children, the group reported.

The Saudi-led coalition has disputed civilian casualty figures by the United Nations and other groups but, amid international pressure, has accepted blame for some attacks. In one rare admission, the coalition said it was responsible for an airstrike in August on a school bus, also in Saada province, that killed scores, including at least 40 children.

The Sunni Muslim coalition is wary of the Shiite Houthi rebels’ alignment with Iran’s Shiite theocracy, as is the United States, which is providing billions of dollars in weapons, intelligence, training and logistical support to the coalition.

The war has worsened a humanitarian crisis that has pushed millions of Yemenis to the edge of famine and displaced more than 3 million people.

The mounting civilian casualties have played a central role in recent votes by the U.S. Congress to end American support for the war, largely symbolic moves given that President Trump has said he would veto the measures.