Islamic State group extremists killed a U.S. elite Navy SEAL in northern Iraq on Tuesday after blasting through Kurdish defenses and overrunning a town in the biggest offensive the area has seen in months, according to officials.

The slain SEAL was the third U.S. serviceman to be killed in direct combat since the U.S.-led coalition launched a campaign in 2014 to "degrade and destroy" the jihadist group, and is a measure of its deepening involvement in the conflict.

"It is a combat death, of course, and a very sad loss," U.S. Defense Secretary Ash Carter told reporters during a trip to Germany.

The SEALs are considered to be among the most able U.S. special operations forces and are capable of taking on dangerous missions.

A senior official within the Kurdish Peshmerga forces facing Islamic State in northern Iraq said the man had been killed near the town of Tel Asqof, around 28 kilometers (17 miles) from the militant stronghold of Mosul.

The Islamic State insurgents occupied the town at dawn on Tuesday but were driven out later in the day by the Peshmerga. A U.S. military official said the coalition had helped the Peshmerga with air support from F-15 jet fighters and drones.

The Kurdistan Region Security Council also announced that at least 25 Islamic State vehicles had been destroyed on Tuesday and more than 80 militants killed. At least 10 Peshmerga also died in the fighting, according to a Kurdish official who posted pictures of the victims on Twitter.