ABS, Yemen — On an August morning, a taxi driver in northwestern Yemen hugged his kids and jokingly told his family, “Forgive me if I don’t come back.” It was his way of laughing off the danger of driving in a country where airstrikes can hit any road at any time.

In the afternoon, Mohammed al-Khal happened upon just such a strike. Three missiles had hit a highway, leaving bystanders wounded. Al-Khal took one of them, an ice cream vendor, in his car and rushed him to the nearest hospital, run by the international humanitarian group Doctors Without Borders.

But the warplanes were still hunting.

Moments after al-Khal pulled up at the hospital in the town of Abs, a missile smashed down by his car, just outside the hospital entrance. Al-Khal, a father of eight, was incinerated. The blast ripped through patients and family waiting in an outdoor reception area. Nineteen people were killed, along with two civilians killed on the highway.

The Aug. 15 attack typified what has been a pattern in the nearly 2-year-old air campaign by Saudi Arabia and its allies against Yemen’s Shiite rebels, known as Houthis. Rights groups and U.N. officials say the U.S.-backed coalition has often either deliberately or recklessly depended on faulty intelligence, failed to distinguish between civilian and military targets and disregarded the likelihood of civilian casualties.

Experts say some of the strikes amount to war crimes.