One of the largest counterterrorism operations against the Islamic State in Iraq in recent years killed four top insurgent leaders last month, the U.S. military said on Friday, dealing the group a major blow at a time when its attacks in Iraq and Syria are on the rise.

The raid by American and Iraqi commandos against several Islamic State hide-outs in western Iraq on Aug. 29 killed at least 14 insurgents and devastated the group’s top leadership in the country, according to a statement from the Pentagon’s Central Command and U.S. counterterrorism officials.

A main target killed was Abu Ali al-Tunisi, a Tunisian national who was the subject of a $5 million reward from the U.S. government, the military revealed on Friday. Mr. al-Tunisi has been ISIS’s most significant designer, manufacturer and teacher in explosives — including improvised devices, suicide vests and car bombs, counterterrorism officials said.

Also killed were the top ISIS commander for all operations in Iraq and two senior commanders for operations in western Iraq, the military’s statement said.

“The raid appears to have effectively killed off ISIS’s entire command in Anbar,” Charles Lister, the director of the Middle East Institute’s Syria and counterterrorism programs, wrote in a Substack newsletter, “Syria Weekly,” on Friday. Anbar is a vast province in western Iraq that has been a locus for violent Sunni extremists for years.

Central Command and the Iraqi military offered scant details when they announced the raid on Aug. 30, even though it was one of the most sweeping counterterrorism missions in the country in years.