US Secretary of State Mike Pompeo addressed the upcoming summit between the United States and North Korea during a press briefing alongside Chinese Foreign Minister Wang Yi in Washington DC on Wednesday, as doubt remains over whether or not it will take place.

Secretary of State Mike Pompeo and Chinese State Councilor and Foreign Minister Wang Yi participate in a press availability, at the Department of State on May 23, 2018.

Visiting Washington, Chinese State Councillor Wang Yi told Secretary of State Mike Pompeo that if the United States seeks peace with North Korea and wants to make history, "now is the time" for the two countries' leaders to hold their first-ever summit.

White House aides are preparing to travel to Singapore this weekend for a crucial meeting with North Korean officials to discuss the agenda and logistics for the summit, U.S. officials said, speaking on condition of anonymity.

The U.S. delegation, which includes White House Deputy Chief of Staff Joseph Hagin and deputy national security adviser Mira Ricardel, was being dispatched after Trump said on Tuesday there was a "substantial chance" the summit would be called off amid concerns Pyongyang is not prepared to give up its nuclear arsenal.

Trump did not say, however, whether the preparatory talks between U.S. and North Korean officials in coming days were expected to clarify the situation.

Pompeo said on Wednesday the United States is prepared to walk away from nuclear negotiations with North Korea if the summit heads in the wrong direction.

Pompeo said he was "very hopeful" the summit would take place but said the decision was ultimately up to Kim, who the secretary of state has met twice in less than two months.

Trump raised doubts about the summit in talks on Tuesday with South Korean President Moon Jae-in, who came to Washington to urge Trump not to let a rare opportunity with reclusive North Korea slip away.

It was unclear whether Trump was truly backing away from the summit or whether he was strategically coaxing North Korea to the table after decades of tension on the Korean peninsula and antagonism with Washington over its nuclear weapons programme.