Pompeo did not name the summit venue. Vietnam had said last week it had not been informed about any time or venue for a possible Trump-Kim summit, but that it was confident in its ability to host such a meeting.
Officials and diplomats had said two weeks ago that Vietnam was keen to host the summit and two sources told Reuters that Hanoi was preparing to receive Kim on a state visit.
Singapore, where Trump and Kim met in June, and Bangkok have also been talked about as possibilities for the planned summit.
Last June's summit - the first between a sitting US president and a North Korean leader - produced a vague commitment by Kim to work toward the denuclearisation of the Korean Peninsula, but he has yet to take what Washington sees as concrete steps in that direction.
Officials and diplomats had said two weeks ago that Vietnam was keen to host the summit