In previous cases, detainees have been set free into the care of high-profile US visitors
Pompeo in Pyongyang with detainees on agenda
America's top diplomat Mike Pompeo held meetings with senior North Korean officials in Pyongyang on Wednesday, with speculation swirling around the fate of three US detainees ahead of a planned US-North Korea summit.
Mr Pompeo was dispatched on an unannounced visit - his second in weeks, but first as secretary of state - to advance preparations for President Donald Trump's unprecedented meeting with Kim Jong Un over North Korea's nuclear arsenal.
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.
Mr Pompeo's visit came with rumours flying over three US citizens being held in the North, fuelled by South Korea where the president's office said they expected the men to be freed.
The trio are a significant domestic political issue in the US and Mr Trump 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."
But the American president spoke as he 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.
Mr Pompeo's itinerary - including whether he would meet the North Korean leader in Pyongyang - was not clear.
He told reporters he would look to prepare for the summit between Mr Trump and "Chairman Un", prompting mockery from observers.
"Pompeo doesn't know the surname is Kim, but he's definitely on top of all the conceptual and semantic nuances associated with the phrase 'denuclearisation of the Korean Peninsula'," arms control specialist Jeffrey Lewis tweeted derisively.
Also on Wednesday, Japanese Prime Minister Shinzo Abe and Chinese Premier Li Keqiang backed the Panmunjom Declaration at a tripartite summit with Mr Moon in Tokyo.
"We reached the common recognition that the complete denuclearisation of the Korean peninsula, (and) the permanent establishment of peace and development of the intra-Korean relations are crucial," Mr Moon said in a statement after the talks, with a formal declaration expected later.
But consensus glossed over the differences between the three neighbours, which have differing positions on the North.
Japan has by far the hardest line of the trio, and has found itself largely watching the diplomatic frenzy from the sidelines, left uneasy by the pace of events and by what it sees as an unwarranted softening towards an untrustworthy Pyongyang.
After the talks, Mr Abe said he hoped to see the international community press Pyongyang to take "concrete steps towards complete denuclearisation of the Korean peninsula", and once again called for a resolution to the hugely emotive issue of Japanese citizens kidnapped by the North.