Hundreds of Iraqi soldiers were trapped or missing Sunday after a chaotic retreat from an army base in western Iraq, military officials said, underscoring the ability of Islamic State insurgents to remain on the offensive despite expanded airstrikes by the United States.

At least 820 soldiers were stationed at Camp Saqlawiyah in Anbar province, north of the insurgent-controlled Iraqi city of Fallujah, when it came under attack from five suicide bombings Sunday afternoon, said Lt. Col. Ihab Hashem, a deputy commander with the Iraqi army’s 8th division who was at the camp. Two bombers drove explosives-packed armored vehicles and three others detonated vests, he said.

In a statement Sunday night, Iraq’s Defense Ministry confirmed that it had lost contact with some of its “heroic soldiers” during operations in Anbar but did not give numbers. It vowed to continue to “clean every inch of land” of militants.

Five battalions had been stranded at the base without supplies for six days after Islamic State militants seized a bridge that was the last access route to the camp. Soldiers said they were forced to boil water from a muddy stream and had been running low on ammunition when the bombings occurred.

“We lost control,” Hashem said after crossing territory controlled by the Islamic State to reach another army base. “We couldn’t gather to retreat. Some are dead, others stayed.”

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He said retreating soldiers had abandoned their vehicles and were traversing enemy territory in small platoons.

“Some are still crossing. They are walking through the trees and houses trying to hide from the insurgents.”

The Islamic State has carried out mass executions of seized Iraqi troops in the past. Iraqi officials say the group massacred 1,700 soldiers at Camp Speicher near the northern city of Tikrit in June.

The latest advance comes despite stepped-up U.S. airstrikes against militants. France launched airstrikes against the extremists last week.

Iraqi military officials said U.S. jets gave air support to a failed army effort to reach the stranded soldiers Sunday morning. U.S. Central Command, however, did not announce details of operations in the area.

Only about 25 percent of the soldiers at Saqlawiyah had managed to reach safety at the nearby 1st division base at Camp Tariq, Hashem said.

“The situation is very bad,” said Lt. Col. Abdulwahab al-Saidi, head of counterterrorism operations for Anbar.

A solider who remained at Saqlawiyah, and who spoke on the condition of anonymity because he was not authorized to talk to the news media, said when reached by phone that just 50 or 60 soldiers were still at the camp, stranded with no vehicles. He put the number of suicide bombings by vehicle at three.

“We don’t have enough ammunition here to defend ourselves,” he said. “Maybe we can last a day.”

Mustafa Salim contributed to this report.