"There will be several steps (which) will be necessary to agree on the location and the scope of those discussions. We have not heard anything directly back from North Korea although we expect to hear something," he said in the Nigerian capital Abuja.

"These are all questions people are anxious to hear answers to. I would say, 'remain patient'."

Pyongyang has been silent since last Thursday's blockbuster announcement in Washington that US President Donald Trump and North Korean leader Kim Jong Un will meet by the end of May to discuss the nuclear standoff in the Korean peninsula.

Trump on Saturday predicted "tremendous success" in the talks and suggested North Korea wanted to "make peace".

Analysts caution that some key answers are needed before the groundbreaking meeting will go ahead, including agreement on the location of the summit and the agenda.