The U.S. military said Monday it killed dozens of Islamic State fighters in airstrikes on two training camps in Yemen.

In a statement, the Pentagon said the strikes disrupted the Islamic State group's attempts to train new fighters to conduct attacks using AK-47s, machine guns and rocket-propelled grenades.

The statement was not specific about how the U.S. attacks were conducted, but a defense official said they were carried out by drones. The official was not authorized to publicly discuss details and spoke on condition of anonymity.

The U.S. has no combat troops in Yemen but has periodically conducted airstrikes to attack militants, including fighters of al-Qaida in the Arabian Peninsula.

Yemen fell into chaos following its 2011 Arab Spring uprising that removed longtime autocrat Ali Abdullah Saleh, now allied with Shiite rebels from the north who occupy much of the country and are fighting his successor. A Saudi-led coalition has been battling the rebels and Saleh's forces since March 2015.

Al-Qaida has taken advantage of the security breakdown to seize territory and expand operations in impoverished Yemen, which sits along strategic oil shipping routes.