Three Korean Americans — Kim Dong-chul, Kim Hak-song and Tony Kim — have been accused of various acts considered hostile to the government. Trump and his lawyer, Rudolph W. Giuliani, have dropped hints recently that they could be freed soon.

“A lot of good things have already happened with respect to the hostages,” Trump said at the White House on Friday. “And I think you’re going to see very good things.”

One of the prisoners, Kim Dong-chul, a former Virginia resident in his mid-60s, was detained in October 2015, while the other two were detained after Trump took office.

In an interview with two reporters traveling with him aboard his plane, Pompeo said he plans to raise again the U.S. desire that the three men be freed, adding, “I’d be a great gesture if they’d agree to do so.”

The main purpose of Pompeo’s visit to North Korea is to finalize an exact time and location for the summit between Trump and the North Korean leader, how long their talks will last and to clarify expectations.

“We also want to make sure what our expectations are not,” Pompeo said. “We are not going to head down the path we headed down before. We will not relieve sanctions until such time as we have achieved our objectives. We’re not going to do this in small increments, where the world is coerced into relieving economic pressures.”

Pompeo left Washington from Joint Base Andrews late Monday on a trip that was not announced by the State Department. He was accompanied by several other senior officials, including Brian Hook, head of State’s policy planning division, and Matthew Pottinger, the senior Asia director at the National Security Council.

In his second visit to North Korea in as many months, and his first as secretary of state, Pompeo is flying into one of the world’s most reclusive countries with no assurances of exactly who he will meet. During his last visit over Easter, when he was CIA director, Pompeo met with Kim Jong Un in an effort to assess what a summit might accomplish.

Just before he landed in Japan for refueling, Pompeo said he doesn’t know exactly who he will see this time. “We’re prepared to meet anyone who can speak on behalf of the North Korean government and give us solid answers so we’re prepared.”

Pompeo’s return to North Korea comes in what it only his second week as the administration’s top diplomat. Arrangements were made in great secrecy befitting a former CIA head. Pompeo has promised to “bring back the swagger” to a State Department that has been sidelined in some foreign policy debates. His high-profile visit appears to be a splashy step in that direction.

Pompeo may get an earful of complaints from the officials he meets. Pyongyang has been disgruntled over what it called “misleading” assertions from some U.S. officials that North Korea is considering denuclearization because of its fear of U.S. military prowess and to alleviate punishing sanctions — a “maximum pressure campaign” laid by Pompeo’s predecessor, Rex Tillerson, who was fired by Trump in March.

North Korea made its displeasure clear Sunday, the day before Pompeo departed Washington. A spokesman for its foreign ministry labeled the U.S. claims of credit for the apparent shift in North Korean policy a “dangerous attempt” to upset detente between two nations whose leaders only a few months ago were threatening nuclear war.

U.S. officials have sought to tamp down expectations that Pompeo will be able to secure the release of the prisoners who were recently transferred from a labor camp to a hotel outside Pyongyang, further raising hopes their release is imminent

Now, with a high-level summit only weeks away, U.S. officials have increasingly urged North Korea to release the three American prisoners in advance.

Last weekend, national security adviser John Bolton told Fox News Sunday, “If North Korea releases the detained Americans before the North-U. S. summit, it will be an opportunity to demonstrate their authenticity.”

The end of their incarceration in a country known for its brutality to prisoners would close a long chapter in hostilities between the United States and North Korea, a period during which U.S. officials accused Pyongyang of using American citizens as bargaining chips.

At least 16 U.S. citizens have been arrested in North Korea since the 1990s. Several of them have been subjected to show trials and forced to make public confessions to crimes against the state. Most served part of their sentences before being released, usually after visits from high-profile Americans such as former presidents Bill Clinton and Jimmy Carter.

Last summer, North Korea turned over custody of University of Virginia student Otto Warmbier, who returned home to Cincinnati in a coma after 17 months in captivity after being detained during an organized tour of Pyongyang. Warmbier died a few days later, and Trump has highlighted his death in several major speeches, including the State of the Union address in January and remarks to the South Korean general assembly last fall.