WASHINGTON - US President Donald Trump acknowledged on Wednesday it was unclear if his planned summit with Democratic People's Republic of Korea (DPRK)'s top leader Kim Jong-un would go ahead, and said Washington would insist that DPRK give up its nuclear weapons despite Pyongyang's threat to pull out of the meeting.

DPRK threw the June 12 summit into doubt on Wednesday, saying it might not attend if Washington continues to demand that it unilaterally abandon its nuclear weapons. North Korea also called off high-level talks with the Republic of Korea (ROK) scheduled for Wednesday, blaming US-ROK military exercises.

"We'll have to see," Trump told reporters in the Oval Office when asked if the summit was still on.

"No decision, we haven't been notified at all ... We haven't seen anything, we haven't heard anything," he added, while saying that he would continue to push for the denuclearization of the Korean Peninsula.

Cancellation of the summit, the first meeting between a serving US president and a DPRK's leader, would deal a major blow to what would be the biggest diplomatic achievement of Trump's presidency.

Trump has raised expectations for success even as many analysts have been sceptical about the chances of bridging the gap due to questions about DPRK's willingness to give up a nuclear arsenal that it says can hit the United States.

The White House said earlier it was still hopeful the summit would take place, but Trump was prepared for a tough negotiation.

"The president is ready if the meeting takes place," White House spokeswoman Sanders told Fox News. "If it doesn't, we'll continue the maximum pressure campaign that's been ongoing."

Sanders said the DPRK's comments were "not something that is out of the ordinary in these types of operations."

DPRK's first vice-minister of foreign affairs, KimKye Gwan, on Wednesday cast doubt on whether the planned meeting between leader Kim Jong-un and Trump, which is set for Singapore, would be held.

"If the U.S. is trying to drive us into a corner to force our unilateral nuclear abandonment, we will no longer be interested in such dialogue and cannot but reconsider our proceeding to the...summit," he said.

He specifically criticized US National Security Adviser John Bolton, who has called for DPRK to quickly give up its nuclear arsenal in a deal that would mirror Libya's abandonment of its program for weapons of mass destruction.

DPRK clashed with Bolton when he worked under the Bush administration.

"We shed light on the quality of Bolton already in the past, and we do not hide our feeling of repugnance towards him," Kim, the vice-minister, said.

Sanders appeared reluctant to endorse the Libya model that the outspoken and hawkish Bolton has touted, most recently on US television on Sunday.

She said the model that would be followed in dealing with DPRK was "the President Trump model."

"He's going to run this the way he sees fit. We're 100 percent confident...he's the best negotiator."

A US official said the DPRK's statements had taken the White House off guard after DPRK's leader Kim's diplomatic outreach both to the United States and ROK.

Reuters