A United Nations expert who irked the Philippines with a surprise visit said Saturday that she was keen to return and investigate alleged summary killings, but only if President Rodrigo Duterte drops his condition that she must hold a debate with him.

Agnes Callamard, U.N. special rapporteur on extrajudicial killings, has been vocal about allegations of systematic executions in the Philippines as part of Duterte's war on drugs. Thousands have been killed since he came to power in June last year.

A planned visit by Callamard in December was cancelled because she refused to accept Duterte's conditions.