The White House tried to swat away criticism that the US is getting nothing in exchange for agreeing to a historic face-to-face summit between president Donald Trump and North Korean leader Kim Jong Un.

White House press secretary Sarah Huckabee Sanders said North Korea has made promises to denuclearise, stop its nuclear and missile testing and allow joint US-South Korean military exercises.

But questions remained over exactly what North Korea means by “denuclearise” and what the US might be risking with a highly publicised summit that will build up Kim’s stature among world leaders.

“Let’s not forget that the North Koreans did promise something,” Ms Sanders said, responding to a reporter’s question about why Mr Trump agreed to a meeting — unprecedented between leaders of the two nations — without preconditions.

She added: “We are not going to have this meeting take place until we see concrete actions that match the words and the rhetoric of North Korea.”

Still, the White House indicated that planning for the meeting was fully on track.

“The deal with North Korea is very much in the making and will be, if completed, a very good one for the World. Time and place to be determined,” Mr Trump tweeted on Friday evening.

The previous night’s announcement of the summit marked a dramatic turnaround after a year of escalating tensions and rude insults between the two leaders.

A personal meeting would have been all but unthinkable when Mr Trump was being dismissed as a “senile dotard” and the Korean “rocket man” was snapping off weapons tests in his quest for a nuclear arsenal that could threaten the US mainland.

The European Union, Russia and China — whose leader spoke by phone with Mr Trump on Friday — have all welcomed the move to hold talks.

North Korea’s government has yet to formally comment on its invitation to Mr Trump. South Korea said the president agreed to meet Kim by May, but Ms Sanders said Friday that no time and place had been set.

The “promises” on denuclearise and desisting from weapons tests were relayed to Mr Trump by South Korean officials who had met with Mr Kim on Monday and brought his summit invitation to the White House.

Mr Trump discussed the offer with top aides on Thursday. Some expressed their reservations but ultimately supported the president’s decision to accept it, according to US officials.

Still, some politicians and foreign policy experts voiced scepticism about the wisdom of agreeing to a summit without preparations by lower-level officials, particularly given the lack of trust between the two sides.

North Korea is also holding three American citizens for what Washington views as political reasons.

“A presidential visit is really the highest coin in the realm in diplomacy circles,” said Bruce Klingner, a Korea expert at the conservative-leaning Heritage Foundation, adding that Mr Trump “seemed to spend it without getting anything in return, not even the release of the three US captives.”