Pompeo was on his second trip to North Korea, laying the groundwork for a summit between Trump and North Korea's Kim Jong Un - only the second sitting secretary of state to visit the country and the highest ranking USA official to meet the young North Korean leader.
The development comes amid easing tensions between the US and North Korea and ahead of a planned meeting between Trump and North Korean dictator Kim Jong Un.
The meeting came as United States Secretary of State Mike Pompeo flew to Pyongyang, the North Korean capital, on an unannounced visit.
The detainees are returning to the United States as Trump prepares to make history by becoming the first sitting US President to meet face-to-face with a North Korean leader.
The three U.S. detainees being released are Korean-American missionary Kim Dong-chul, Kim Sang-duk - also known as Tony Kim - and Kim Hak-song.
Tony Kim was detained at Pyongyang's airport in April 2017 and accused of unspecified "hostile acts" against the regime.
Of the newly released detainees, Kim Dong Chul, a South Korean-born USA citizen, had been held the longest. The families of all three men say they were innocent of the allegations.
Sol said he's thankful that President Trump's administration is publicly bringing up his father's case, but as time goes by the stress of the situation is wearing him down.
Speaking to reporters as he returned from North Korea, Pompeo said his meetings with the North Koreans were "very productive".
The former prisoners had been jailed in North Korea for over a year.
Satellite photos show lava-oozing volcano fissures in Hawaii
In this image, vegetation is shown in red and yellow and green mark hot places where lava is flowing or magma is near the surface. ASTER has also been watching sulfur dioxide gas produced by the volcano through eruptions and quieter cracks in the ground.
American student Otto Warmbier, held for allegedly trying to steal a propaganda poster from a hotel, died shortly after being returned home in a coma past year.
Japan fears it may be left out of North Korean negotiations, with Abe and Kim yet to set up a summit.
He also said Pompeo had a "good meeting with Kim Jong Un".
Kim, a naturalized U.S. citizen, was born in Jilin, China, one of the provinces that borders North Korea, and is ethnically Korean.
Kim noted the improved relations between the Koreas, as well as the North's policy to "concentrate all efforts into economic progress" in the country. He said he hoped North Korea would "do the right thing".
He is a South Korean-born USA businessman and pastor arrested in October 2015.
"All indications are their health is as good as could be given they been through", said Pompeo.
In talks with Moon later on Wednesday, Abe expressed Japan's concern that pressure on North Korea might be lifted too early as a "reward" for its shutting down its nuclear test site or halting missile launches.
"We can not forget: No regime has the right to hold American citizens in captivity without cause, and under no circumstances should American citizens be viewed as bargaining chips", Schumer said on the Senate floor.
Abe called for additional, specific action, a spokesman for South Korea's presidential office said in a Tokyo briefing. Some 28,500 US forces are based in the allied nation, a military presence that has been preserved to deter North Korea since the war ended in 1953 without a peace treaty.