Washington (CNN) Americans should anticipate more military operations in Africa as the war on terrorism continues to morph, Sen. Lindsey Graham warned Friday.

"This war is getting hot in places that it's been cool, and we've got to go where the enemy takes us," Graham told reporters on Capitol Hill.

The South Carolina Republican's comments came after a meeting with Defense Secretary James Mattis and followed the news that four US servicemen were killed in action in Niger in an ambush by ISIS fighters.

"The war is headed to Africa, Graham said. "It's beginning to morph. As we suppress the enemy in the Mideast, they're going to move, they're not going to quit."

Graham also said "the rules of engagement are going to change," and explained that the US approach to counterterrorism operations will be more aggressive, moving to what he called "status-based targeting."

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