WASHINGTON, Oct. 23 -- The U.S.-led strategy to defeat the Islamic State (IS) is working, U.S. Defense Secretary Chuck Hagel said on Thursday, but emphasized that the fight against the terrorist group will be a "complicated, difficult contest."

In an exchange with reporters at the Pentagon after meeting with South Korean Defense Minister Han Min-koo, Hagel said the administration has repeatedly made clear that the fight against IS will be a long, difficult effort.

"We believe that our strategy is working," he said, while acknowledging that progress in Iraq is mixed.

"The reality is that ISIL has control and still does control a significant amount of ground in Iraq and I don't think it's any different from any complicated, difficult contest," the secretary said.

With the U.S.-led coalition continuing to carry out airstrikes against IS targets, Hagel told reporters "there will be mixed and various outcomes daily." However, he added that he saw no reason for changing U.S. policy.

"We think it's working," noted the defense chief.