Secretary of State Mike Pompeo is making a second surprise visit to North Korea, with speculation growing that he will bring home three jailed Americans.
His visit is intended to lay the groundwork for a historic summit between North Korean leader Kim Jong-un and President Donald Trump.
Mike Pompeo told reporters he was hoping to finalize plans for talks, which are likely to focus on denuclearization.
However, the release of the detainees is a central issue for the Americans.
A South Korean presidential official told news agency Yonhap that North Korea was expected to release the US citizens as a “goodwill gesture”.
Mike Pompeo said he hoped Pyongyang would “do the right thing” and release three Americans imprisoned in North Korea.
He said: “We’ve been asking for the release of these detainees for 17 months.”
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North Korea has historically used its foreign prisoners as leverage in its diplomatic dealings.
One of the detainees was jailed in 2015, the other two have been in prison for just over a year. Their convictions have been widely condemned as political and an abuse of human rights.
The last American to be freed – Otto Warmbier, who was jailed for stealing a hotel sign – was released last year but was fatally ill, and died shortly after returning home. The cause of death remains unexplained.
Mike Pompeo said a “good relationship” was formed at the first meeting in April, which marked the highest level US contact with North Korea since 2000.
A state department official travelling with Mike Pompeo said the US would also be “listening for signs from North Korea that things have substantially changed” with the nation’s nuclear ambitions.
Last month, President Trump stunned the international community by accepting North Korea’s suggestion for direct talks – it will be an unprecedented move for a sitting US president to meet a North Korean leader.
President Trump referred to Mike Pompeo’s latest visit while announcing that the US was withdrawing from the nuclear agreement with Iran.