“When the conditions were not good, and there was no security, they did not provide water and food by the contract,” said a border-police colonel, who asked that his name be withheld.

By June 17, the brigade was in position around Qaim, with hopes of blocking ISIS fighters’ free passage to and from Syria. But supplies were so depleted the troops could barely fight. Its members said they were given only a small piece of cake and about 10 ounces of water a day.

Morale sank further, brigade members said, because another unit in Qaim had already run out of water and food, prompting the Ninth Brigade to share its meager stores.

Moreover, the local people refused to help, police officers said, either because they had sided with ISIS or were afraid, and did not want to risk the militants’ wrath.

With supplies almost gone, the brigade commander, Brig. Gen. Sadiq Rasheed Abdilal, left Qaim to complain to senior officers, his troops said. They have not heard from him since. The troops said he had been arrested and his cellphone switched off.

Officers on the brigade staff declined to discuss their commander’s whereabouts.

One colonel offered only that he left for “business in Baghdad.” A spokesman for the Fourth Division said that General Abdilal remained at work, but refused to provide a way to reach him.

On June 22, the troops said, they received an abrupt order to abandon Qaim and head to Waleed. They said they were astounded, because Qaim was essential to Iraq’s defense.