The detainees will be landing at Andrews Air Force Base
North Korea frees three American detainees ahead of Donald Trump and Kim Jong-un summit
The family of one of the Americans freed from North Korea is expressing gratitude for his release.
The family of 59-year-old Toby Kim is thanking "all of those who have worked toward and contributed to his return home." In a statement, the family credited President Donald Trump for engaging directly with North Korea.
"Mostly, we thank God for Tony's safe return," the statement said. It added that the family appreciates "the support and prayers of friends and even strangers during this challenging year."
The statement was forwarded to The Associated Press by Randall Brandt, a spokesman for the family, shortly after Mr Trump announced on Wednesday that three Americans were coming home.
The statement urged people to "continue to pray for the people of North Korea and for the release of all who are still being held."
Mr Trump made the announcement on Twitter, saying "Secretary of State Mike Pompeo is in the air and on his way back from North Korea with the 3 wonderful gentlemen that everyone is looking so forward to meeting."
President Trump added that Mr Pompeo had a "good meeting" with North Korean leader Kim Jong Un.
In another Tweet, Mr Trump said that Mr Pompeo and the detainees will be landing at Andrews Air Force Base at 2 am on Thursday. He says "I will be there to greet them. Very exciting!"
The trio are a significant domestic political issue in the US and Mr Trump had already hinted last week of imminent news after sources said they had been relocated.
In previous cases, detainees have been set free into the care of high-profile US visitors, but there was no immediate indication they would be released after Mr Pompeo held talks with Kim Yong Chul, director of the North's United Front department.
The rapid detente on the Korean peninsula triggered by the Winter Olympics is a marked contrast from last year, when Mr Kim and Mr Trump traded personal insults and threats of war over the North's nuclear and ballistic missile programmes.
"We think relationships are building with North Korea," Mr Trump said in televised comments from the White House. "We will see how it all works out. Maybe it won't. But it can be a great thing for North Korea, South Korea and the entire world."
Mr Trump is planning a historic summit with the North Korean leader.
He told reporters that he hoped to agree a date and venue for the summit - even though Mr Trump said they had already been chosen.
But optimism over the process was dealt a blow by Mr Trump's pullout from a nuclear deal with Iran on Tuesday. The American president yanked the US out of a nuclear deal with Iran, complicating the prospects of persuading Pyongyang to surrender its atomic arsenal.
Mr Trump poured scorn on the "disastrous" 2015 accord, reached after a decade and a half of careful diplomacy by Britain, China, France, Germany, Iran, Russia and past US administrations, describing it as an "embarrassment" to the United States.
Other signatories and the International Atomic Energy Agency say Iran has complied with its obligations under the deal.
Adam Mount of the Federation of American Scientists said: "Amazing to think that Secretary Pompeo will arrive in Pyongyang today bearing the following message: 'If you eliminate your nuclear weapons, we'll lift sanctions and won't attack you. You can trust us'."
The details of any North Korean deal appear to be still under discussion.
At a historic meeting in the Demilitarised Zone last month, Mr Kim and South Korean President Moon Jae-in reaffirmed their commitment to a "common goal" of "complete denuclearisation" of the Korean peninsula in their Panmunjom Declaration.
On Tuesday, Mr Kim met Chinese President Xi Jinping in China - the second time in six weeks - highlighting efforts by the Cold War-era allies to mend frayed ties, and with Beijing keen to avoid being left out in the cold.
China's official Xinhua news agency cited Mr Kim as telling Mr Xi there was no need for North Korea to be a nuclear state "as long as relevant parties abolish their hostile policies and remove security threats against" the country.
Mr Kim also expressed hope that the US and North Korea would take "phased and synchronous measures", signalling Pyongyang wanted a quid pro quo.