"We have said... and the president has said this, that in the fight against ISIL (the acronym for the Islamic State), this is not a fight with Muslims or Islam," said Carter in a joint press conference with visiting Indian Minister of Defense Manohar Parrikar.

"This (IS) is an extremist, violent movement which threatens America and needs to be defeated," said Carter. "We're working on accelerating the defeat of ISIL. That's the important thing."

During his congressional hearing at the Senate Armed Services Committee Wednesday, Carter said the United States was "at war."

Pentagon chief says anti-IS fight is not fight with Muslims or Islam

"The reality is we're at war. That's how our troops feel about it because they're taking the fight with ISIL every day," said Carter Wednesday.

Also during his hearing Wednesday, Carter said the Pentagon was prepared to assist the Iraqi government with more personnel and attack helicopters to retake the important Iraqi city of Ramadi from the IS.

The Iraqi forces in May lost Ramadi to IS fighters, triggering an unusual anger from Carter, who at that time accused the Iraqis of lacking "will to fight."

Carter's remark Wednesday was the latest sign of U.S. willingness to intensify its involvement in the fight against the IS.

However, Carter on Thursday refused to predict when Ramadi would be retaken by the Iraqis.

"It has been disappointingly slow, so I'm reluctant to make a time projection," said Carter. "A general answer to that kind of question is as soon as possible."