WASHINGTON (REUTERS) - US President Donald Trump said on Wednesday (May 23) he would know next week whether his summit with North Korean leader Kim Jong Un would take place on June 12 in Singapore as scheduled, casting further doubt on plans for the unprecedented meeting.

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, US officials said, speaking on condition of anonymity.

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.

The US 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.

A White House spokesman said the meeting hosts in Singapore have been "extremely gracious", and are committed to helping both the US and North Korean delegations get ready, NPR reported.

Asked on Wednesday whether the summit would go ahead, Trump told reporters: "It could very well happen. Whatever it is, we'll know next week about Singapore. And if we go, I think it will be a great thing for North Korea."

But he added: "We'll see."

Trump did not say, however, whether the preparatory talks between US and North Korean officials in the 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.

The White House was caught off guard when, in a dramatic change of tone, North Korea last week condemned the latest US-South Korean air combat drills, suspended North-South talks and threatened to scrap the summit if Pyongyang was pushed toward "unilateral nuclear abandonment".

If the summit is called off or fails, it would be a major blow to what Trump supporters hope will be the biggest diplomatic achievement of his presidency.

'BAD DEAL IS NOT AN OPTION'

Pompeo insisted the Trump administration was "clear-eyed"about North Korea, which has a history of making promises in negotiations and then backtracking.

"A bad deal is not an option," Pompeo said in his written opening statement for a House of Representatives Foreign Affairs Committee hearing. "If the right deal is not on the table, we will respectfully walk away."

Pompeo, who was director of the Central Intelligence Agency before becoming secretary of state in April after Trump fired Rex Tillerson, is the highest-ranking Trump administration to meet Kim. On his most recent trip, he brought back three Americans who had been held by North Korea.

Pompeo said a US-led sanctions pressure campaign would not be eased until North Korea gives up nuclear weapons.

"We have made zero concessions to Chairman Kim and have no intention to do so," he said.

"Our posture will not change until we see credible steps taken towards the complete, verifiable and irreversible denuclearisation of the Korean peninsula," he said.

Meeting Wang later in the day, Pompeo said the United States expects all countries, including China - North Korea's main trading partner and ally - to "meet their obligations" to enforce sanctions on Pyongyang.

In response to a question on whether the summit will take place on June 12, Pompeo said:"We're still working, driving towards the date. I hope that it takes place. Chairman Kim requested a meeting. We - President Trump agreed. We worked to find a date and a location, we had it settled, and I'm hopeful.

"What I can say for sure is our team is preparing up and down the administration. The President will absolutely be prepared for the meeting as well, and I hope that we can have this opportunity, this historic opportunity to do something that would truly transform this global challenge that's been threatening the world for an awfully long time."

Wang said China hopes the Trump-Kim summit will take place as scheduled.

Trump suggested on Tuesday that Kim's recent meetings with Chinese President Xi Jinping had influenced Kim to harden his stance ahead of the summit. China's foreign ministry said, however, that Beijing had played a positive role on the Korean peninsula.

Also on Wednesday, a United Nations Security Council committee approved travel by North Korean officials to Singapore for the summit, diplomats said. Singapore had asked the UN sanctions panel for a blanket waiver for the North Koreans' participation.