White House national security adviser John Bolton said Tuesday that North Korea has not made progress toward denuclearization, a stark assessment of President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE's efforts to secure a nuclear agreement with North Korean leader Kim Jong Un.

“The United States has lived up to the Singapore declaration,” Bolton said in an interview on Fox News, referring to the framework Trump and Kim agreed to during their summit in June. “It’s just North Korea that has not taken the steps we feel are necessary to denuclearize.”

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Bolton said the U.S. will not lift economic penalties on North Korea until the country shows greater progress toward disassembling its nuclear and ballistic missile programs.

“The idea that we’re going to relax the sanctions just on North Korea’s say-so, I think, is something that just isn’t under consideration,” Bolton said. “We’re going to continue to apply maximum pressure to North Korea until they denuclearize, just as we are to Iran. The president feels very strongly about it.”

Bolton's assessment stands in contrast to Trump's attempts to reassure skeptics that Kim will honor the Singapore agreement, in which he committed to "work towards complete denuclearization of the Korean Peninsula."

"There is no longer a nuclear threat from North Korea,” the president proclaimed on Twitter following the June meeting in Singapore. “Meeting with Kim Jong Un was an interesting and very positive experience. North Korea has great potential for the future!"

Trump last month tweeted that he had "confidence that Kim Jong Un will honor the contract we signed &, even more importantly, our handshake."

Since then, however, progress toward denuclearization has appeared to be uneven, at best. Media reports citing U.S. intelligence estimates say Pyongyang continues work on ballistic missile and nuclear weapons development.

The U.S. has won some smaller victories, including North Korea's dismantlement of a nuclear-launch site and returning the remains of more than 50 U.S. troops who served in the Korean war.

Asked last week if Trump is satisfied with North Korea's progress toward denuclearization, White House press secretary Sarah Huckabee Sanders said the president "won't be completely satisfied until all of Korea has been denuclearized."

"We're going to continue moving forward," she added. "We've seen steps of progress and continued cooperation. We're incredibly grateful and thankful for the remains of the service members that were returned yesterday. And we're going to continue to work with North Korea."

Talks on North Korea's nuclear program have continued behind the scenes.

Trump last Wednesday received a letter from Kim, and Secretary of State Mike Pompeo Michael (Mike) Richard PompeoPutin nominated for Nobel Peace Prize The Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' Pompeo accused of stumping for Trump ahead of election MORE handed a response letter to North Korean Foreign Minister Ri Yong Ho last week at an Asia summit meeting.

Bolton said Tuesday that Trump's letter to Kim contained a proposal for Pompeo to visit Pyongyang to meet again with the North Korean leader.

“The president’s prepared to meet at any point,” Bolton said. “But what we really need is not more rhetoric. What we need is performance from North Korea on denuclearization.”