WASHINGTON -- The United States aspires to have North Korea as a "close partner" and not an enemy, Secretary of State Mike Pompeo said Friday, noting that the U.S. has often in history become good friends with former adversaries. Pompeo said he had told North Korean leader Kim Jong Un of that hope during his brief visit to Pyongyang earlier this week, where he also he finalized details of the upcoming summit between Kim and U.S. President Trump and secured the release of three Americans imprisoned in the country.

Pompeo also said his talks with Kim on Wednesday were "warm," ''constructive," and "good" -- and that he made clear that if North Korea gets rid of its nuclear weapons in a permanent and verifiable way, the U.S. is willing to help the impoverished nation boost its economy and living stands to levels like those in prosperous South Korea.

"We had good conversations about the histories of our two nations, the challenges that we have had between us," Pompeo told reporters at a news conference with South Korea's visiting foreign minister Kang Kyung-wha Friday. "We talked about the fact that America has often in history had adversaries who we are now close partners with and our hope that we could achieve the same with respect to North Korea."

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He did not mention other adversaries by name, but Pompeo and others have often noted that the U.S. played a major role in rebuilding Japan and the European axis powers in the wake of the Second World War. With U.S. help, those countries recovered from the devastation of conflict.

"If North Korea takes bold action to quickly denuclearize, the United States is prepared to work with North Korea to achieve prosperity on the par with our South Korean friends," he said.

On Thursday, Mr. Trump said he will be meeting with Kim on June 12, tweeting "we will both try to make it a very special moment for world peace!" The tweet came hours after Mr. Trump led a dramatic overnight welcome ceremony for the three Americans released by North Korea -- Kim Dong Chul, Kim Hak Song, and Tony Kim. After greeting them privately on board a government plane, the president and first lady escorted them in front of cameras.

"One of them walked up to me, shook my hand. I said, 'Welcome home.' He said, 'God bless America,'" said State Department official Brian Hook, who was with Pompeo in North Korea.

Administration officials consider the release an encouraging signal ahead of next month's summit.

"Kim Jong Un has said publicly and in discussions is that he is prepared, he is prepared to negotiate to achieve complete denuclearization of the Korean peninsula," Vice President Mike Pence told "Face the Nation" moderator Margaret Brennan on "CBS This Morning." "Those words are important, but we'll see what they mean."

Kang praised the upcoming meeting between Mr. Trump and Kim in Singapore as an "historic" opportunity, but added a few notes of skepticism as well. Amid concerns that North Korea will demand the U.S. withdraw its troops from neighboring South Korea, Kang emphasized that the U.S. military presence there must be "a matter for the U.S.-ROK alliance first and foremost," using an acronym for South Korea's official name, the Republic of Korea.

She said the U.S. troop presence in the South for the past 65 years has played a "crucial role for deterrence," peace and stability on the Korean peninsula. Therefore, she said, any change in the size of the U.S. forces in the South Korea should not be on the table at the summit.

"The next few weeks will be critical, requiring air-tight coordination between our two countries," Kang said, noting that South Korean President Moon Jae-in would be in Washington to see Mr. Trump later this month.

Since Mr. Trump announced plans to hold a summit with Kim questions have been raised continually about whether the two leaders have the same objective in mind when they speak about "denuclearization." To the U.S., that means the North giving up the nuclear weapons it has already built. But North Korea has said it's willing to talk now because it's already succeeded in becoming a nuclear-armed state, fueling skepticism that the North would truly being willing to give those weapons up.

Pompeo said there would need to be "complete" and "verifiable" denuclearization that would remove North Korea as a threat to the South, the United States and the rest of the world. He said a massive inspection and monitoring regime would be required to ensure the North's compliance.

"I think there is complete agreement about what the ultimate objectives are," Pompeo said, though he declined to offer more detail.