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.

“The Saudis have been committing war crimes in Yemen,” said Gabor Rona, a professor teaching the laws of war at Columbia University. He warned that American personnel helping the coalition “may also be guilty of war crimes.”

Nearly 4,000 civilians have been killed in the war, and an estimated 60 percent of them died in airstrikes by the Saudi-led coalition, the U.N. says.

Saudi Arabia launched the coalition campaign in March 2015 in a bid to restore the internationally recognized government of President Abed Rabbo Mansour Hadi, after the Houthis overran the capital, Sanaa, and the north of the country. The Iranian-backed Houthis are allied with troops loyal to Hadi’s ousted predecessor, Ali Abdullah Saleh.

The war has devastated the country of 26 million, causing widespread hunger and driving 3 million from their homes.

Warplanes have hit medical centers, schools, factories, infrastructure and roads, markets, weddings and residential compounds.

The U.S. and its allies have sold billions of dollars in weapons to Saudi Arabia for the campaign. The U.S. military provides it with intelligence, satellite imagery and logistical help.

Washington underlines it does not make targeting decisions and calls on the coalition to investigate reported violations. Over the summer, the U.S military reduced the number of military personnel advising the coalition from several dozen to fewer than five, an apparent move to distance itself from the campaign.

“U.S. security cooperation with Saudi Arabia is not a blank check,” National Security Council spokesman Ned Price said.

The coalition says it does its utmost to avoid civilian casualties and notes rebels often operate among civilians. Rights groups and U.N. officials have reported probable war crimes by the Houthis, including shelling civilian areas and basing their fighters in schools and other civilian locations.

“This is the fog of war,” the coalition’s spokesman, Saudi Gen. Ahmed al-Asiri, told The Associated Press when asked if there is a pattern of civilian deaths. “In war, there are decisions that should be taken fast.”

The coalition, which says it investigates every claim of violations, has made nine investigations public. In two it acknowledged mistakes and said it would pay compensation to victims. In most of the other cases, it said the strikes were against a justified military target.

But critics say the American and international backing has given Saudi Arabia and its allies a free rein.

“We believe that the coalition understood … it has a green light to commit more massacres in Yemen,” said Abdel-Rashed al-Faqeh, the head of Muwatana, one of Yemen’s most prominent rights groups.