WASHINGTON (Reuters) - North Korea is continuing to produce fuel for nuclear bombs in spite of its pledge to denuclearize, U.S. Secretary of State Mike Pompeo said on Wednesday, even as he argued that the Trump administration was making progress in talks with Pyongyang.

Asked at a Senate Foreign Relations Committee hearing whether North Korea was still making bomb fuel, Pompeo responded to Democratic Senator Ed Markey by saying: “Yes, that’s correct ... Yes, they continue to produce fissile material.”

Pompeo declined to respond when asked whether North Korea was continuing to pursue submarine-launched ballistic missiles or whether its nuclear program was advancing generally.

He said he would be happy to answer the latter question if necessary in a classified setting, but suggested public statements on the issue would not help “a complex negotiation with a difficult adversary.”

Pompeo defended what he termed progress in talks with North Korea stemming from an unprecedented June 12 summit between President Donald Trump and North Korean leader Kim Jong Un in sometimes testy exchanges with skeptical lawmakers from both parties.

He said the United States was engaged in “patient diplomacy” to persuade North Korea to give up its nuclear weapons, but would not let the process “drag out to no end.”

Briefing on his July 5-7 visit to North Korea, Pompeo said he had emphasized this position in “productive” discussions with his North Korean interlocutor, Kim Yong Chol.

He said Trump remained upbeat about the prospects for North Korean denuclearization, but Kim needed to follow through on his summit commitments.

Pompeo said U.S. North Korea policy was guided by a principle stated by Trump on July 17 that “diplomacy and engagement are preferable to conflict and hostility.”

Secretary of State Mike Pompeo arrives to testify before the Senate Foreign Relations Committee on Capitol Hill in Washington, U.S., July 25, 2018. REUTERS/Lucas Jackson

Trump has hailed his summit with Kim as a success, even saying the day after that North Korea no longer posed a nuclear threat, but questions have been mounting about Pyongyang’s willingness to give up a nuclear weapons program that threatens the United States.

Kim committed in a broad summit statement to work toward denuclearization but Pyongyang has offered no details as to how it might go about this.

Pompeo left Pyongyang on July 7 saying he had made progress on key issues, only for North Korea to accuse his delegation hours later of making “gangster-like” demands.

Pompeo reiterated that North Korea had agreed to denuclearize. However, he did not respond when asked by Senator Bob Menendez whether Pyongyang agreed with the U.S. definition of denuclearization, except to say he was fully confident North Korea understood this.

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Menendez, the ranking member of the committee, called Trump’s meeting with Kim “a reality TV ‘summit’ that was little more than a photo-op with a brutal dictator.”

“We have seen only a vague agreement of promises to make more promises - but with weaker commitments than North Korea has previously made,” he said.

Pompeo conceded that there was an “awful long way to go” with North Korea but in answer to a question, said the U.S. goal was for North Korea’s complete, verifiable, irreversible denuclearization by the end of Trump’s current term in office, which runs until January 2021, and “more quickly if possible.”

Trump said last week there was “no rush” and “no time limit” on the denuclearization negotiations, but Pompeo has given varying statements about how patient Washington might be.

He rejected Markey’s suggestion that the United States was being “taken for a ride” by North Korea, replying, “fear not senator, fear not.”

However he indicated that no progress had been made on a key U.S. demand - that North Korea disclose the range of its nuclear capabilities, saying: “An initial declaration ... is something that is at the very forefront of what ... we think, makes sense to get them to a point where we can verify their full denuclearization.”

The Republican chairman of the committee, Bob Corker, criticized Trump for saying that Kim was “very talented” and that “he loves his people,” given the country’s serious human rights abuses and the death of U.S. college student Otto Warmbier after imprisonment there.

“Really?” Corker said.