WASHINGTON -- US Special Representative for North Korea Stephen Biegun said Wednesday that he has not seen concrete evidence that North Korea plans to dismantle its nuclear weapons program but believes Pyongyang can still make that choice.

Biegun made the remark before the US Senate Foreign Relations Committee during a confirmation hearing on his nomination as deputy secretary of state.

He said the belief is shared by US President Donald Trump, who "remains of the view" that North Korean leader Kim Jong-un "can make this decision to move forward."

"Ultimately, it's the North Koreans that have to make the choice," Biegun said, emphasizing that the "window is still open" for a diplomatic solution to the nuclear issue.

"We do not have any verifiable or meaningful evidence that they have yet made that choice. Our hypothesis is they can make that choice," he added, calling on the North Koreans to "seize the moment."

Denuclearization negotiations between Washington and Pyongyang have stalled since a second summit between Trump and Kim in February ended without a deal.

The two sides remain apart on how much the North should denuclearize in order to receive sanctions relief and other concessions from the US.

Biegun, who has led working-level negotiations with Pyongyang, said he plans to continue in his current role if confirmed, and that it would send an important message to the North Koreans about the priority Trump places on the negotiations.

But he also echoed his earlier frustrations about the North Korean negotiating team, saying his counterpart needs to be empowered by the North Korean leader himself.

As his ideal counterpart, Biegun singled out First Vice Foreign Minister Choe Son-hui, who he said has not engaged in meaningful discussions so far.

Choe, meanwhile, renewed calls on the US to drop its "hostile" policy toward the North.

Speaking in Moscow hours before Biegun's hearing, she said she believes the nuclear issue may have been taken off the negotiating table for now.

"I think the nuclear issue can be discussed again when the US abolishes all hostile policies toward North Korea," she said.

Biegun rejected suggestions the US has proposed another summit between Trump and Kim, saying the president has made clear it should be preceded by a "near-deal" at least.

Referring to North Korea's end-of-year deadline for the negotiations, Biegun said the US is not bound to such an "artificial" deadline.

The US "will be at this as long as it takes," he said, adding that if the North Koreans revert to "provocative steps" it would be a "huge mistake and a missed opportunity" for the regime.

Biegun also disagreed with North Korea's characterization of the last round of working-level talks held in Stockholm, Sweden, in October.

He said they were "constructive," although Pyongyang described them as a failure.

On North Korea's recent claim that Biegun proposed another meeting next month, the envoy said the US side would do so only at the invitation of the Swedish government.

Trump and Kim have had three meetings since June 2018 -- two summits and a brief encounter at the inter-Korean border in June -- to try to reach a deal on dismantling Pyongyang's nuclear weapons program.

Their first summit in Singapore produced an agreement committing the North to "work toward" the complete denuclearization of the Korean Peninsula in exchange for US security guarantees.

Biegun admitted the two sides have yet to reach an agreement on how the North will denuclearize, adding the US has been placing "some very, very significant demands in front of the North Koreans."

On Sunday, South Korea and the US announced the postponement of their planned combined military exercises in support of diplomatic efforts to denuclearize the North.

Trump tweeted a message to Kim shortly afterward, urging him to "act quickly" and "get the deal done" before adding, "See you soon!"

The North scoffed at the postponement, saying what it wants is a complete end to the military drills. (Yonhap)