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 hospital in the town of Abs, run by the international humanitarian group Doctors Without Borders.

But the warplanes were still hunting. Moments after al-Khal pulled up at the Abs hospital, hell broke loose. A missile struck just outside the hospital entrance. Al-Khal, a father of eight, was incinerated in his car. 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 in August 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 been devastating for the country of 26 million. Around 3 million have been driven from their homes. The bombardment, fighting and a coalition blockade have caused widespread hunger.

Warplanes have hit medical centers, hospitals, schools, factories, infrastructure and roads, as well as 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 in October.

The coalition says it does its utmost to avoid civilian casualties and notes the rebels often operate among civilians. Rights groups and U.N. officials have also 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 strikes. "In war, there are decisions that should be taken fast."

The coalition says it investigates every claim of violations. So far it 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 and lack of independent investigation have 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.

The strike in Abs underscored several of the problems experts point to in many of the strikes — the failure to distinguish between civilian and military targets and a lack of proportionality, the principle that use of force must be balanced to avoid civilian casualties.

In the strikes, warplanes initially fired a rocket targeting a Houthi checkpoint manned by two rebels on a highway outside Abs. The fighters escaped, but two more rockets were fired, killing two bystanders and wounding others. It appears the warplanes followed al-Khal's Camry, believing he was carrying a wounded fighter, and struck him outside the hospital.

The hospital was on a coalition list of sites not to be targeted in airstrikes, and had markings on its roof to show it was a medical facility.

The AP interviewed witnesses to the strikes on the highway and at the hospital, as well as al-Khal's two wives.

The head of Doctors Without Border's mission in Yemen, Colette Gadenne, said the coalition acknowledged to the group privately that the strike was a mistake.

The head of the coalition's investigation team, Mansour al-Mansour, told the AP he could not discuss the results of the investigation in public. He said the coalition gave Doctors Without Borders all the information it gathered.

The effect of the strike — the fifth to hit a facility run by the group in Yemen — has been wide-reaching. The organization pulled its personnel from northern Yemen, straining staff at multiple hospitals.

The Abs hospital served a population of around 100,000, said its manager, Ibrahim Ali. Now it is shut down and the nearest medical facilities are two or three hours away by car. "Patients sometimes die in the road," Ali said.

Rona, the legal expert, said those behind the Abs strikes "didn't take sufficient precautions to determine that the people in the taxi are targetable." Then, warplanes struck where "there would be significant collateral damage to the hospital."

"Any way you look at it, it is a war crime."


Al-Haj reported from Sanaa, AP journalists Maad al-Zikry and Hani Mohammed contributed to this report from Yemen.