Philippine President Rodrigo Duterte has defended his criticism of the US ambassador to the Philippines, Philip Goldberg, for meddling with Philippine domestic affairs.

Duterte said Goldberg had  criticized him for making a joke about the rape and murder of an Australian missionary during a jail riot in Davao in 1989. Duterte called Goldberg's remarks  highly inappropriate -- but said the US remains a strong ally of the Philippines.

A US State Department spokesperson said Washington is aware of the controversy and that Goldberg is a multi-time ambassador and one of the government's most senior diplomats.