The Philippines moved to shore up relations with the United States on Tuesday with guarantees that a treaty between them would be honored and security ties were "rock solid," despite President Rodrigo Duterte's railings against Washington.

The firebrand leader launched more verbal salvos Monday about what he called atrocities under American colonial rule of the archipelago nation, saying U.S. special forces working in the restive south under a defense treaty should leave because they were complicating counterinsurgency operations.

Duterte is hugely popular at home for his brash comments and take-charge style, but the frequency of his tirades against Washington, including calling President Barack Obama a "son of a bitch" last week, has tested a relationship of strategic importance to both sides.