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 outspoken leader launched more verbal salvos on Monday about what he called atrocities under US colonial rule of the archipelago nation, saying US Special Forces working in the restive south under a defense treaty should leave because they were complicating counter-insurgency operations.

The frequency of Duterte's 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.