North Korea is soon expected to release three US citizens held in the communist state, an official from Seoul's presidential office Cheong Wa Dae said Wednesday, in an apparent goodwill gesture ahead of a historic meeting between its leader Kim Jong-un and US President Donald Trump.

The official said US Secretary of State Mike Pompeo was expected to return with the exact time of the Trump-Kim summit, along with the three US captives in North Korea.

"We expect him to bring the date, time and the captives," the official said, while speaking on condition of anonymity.

Pompeo arrived in Pyongyang earlier in the day, according to reports, marking his second trip to the reclusive North in less than a month.

Trump earlier said the location of his meeting with Kim has already been set.

The US secretary of state earlier said the North's release of the three US citizens would be a "great gesture," noting the US has been asking for their freedom for 17 months.

Pompeo was earlier expected to bring the three captives through the inter-Korean border, but the Cheong Wa Dae official said that will likely not be the case.

The three US citizens are all said to be Korean-Americans. It was not clear when Pompeo was set to leave Pyongyang. (Yonhap)