Senior officials staged a flurry of calls and top-level meetings on Friday as they scrambled to make a proposed nuclear summit between US President Donald Trump and North Korea's Kim Jong Un a reality.
There was no immediate breakthrough, but North Korea's foreign minister was to remain in Stockholm into Saturday for further talks with Swedish leaders, as the Scandinavian intermediary strives to pave the way for talks that could end a threat of nuclear war.
From Washington, Trump called his South Korean counterpart Moon Jae-in, whose government last week passed an apparent summit invitation to Trump from Kim. Trump accepted on the spot and triggered a race to set a credible agenda for what could be a historic breakthrough.
- Rampant skepticism -
At the same time, foreign ministers Kang Kyung-wha of South Korea and Taro Kono of Japan were in Washington for talks at an under-staffed US State Department, left in turmoil by Trump's abrupt and brutal Twitter-sacking of former secretary of state Rex Tillerson.
"I think we're cautiously optimistic that the talks will happen and that this will be a breakthrough for a peaceful resolution of the North Korean nuclear issue," Kang told the PBS NewsHour.
The abrupt decision to accept the summit has triggered much skepticism from Korea observers but, after his call with Moon, Trump's White House remained cautiously optimistic that his strategy of making military threats backed by crippling real-world sanctions had forced Kim's hand.
Trump and Moon "agreed that concrete actions, not words, will be the key to achieving permanent denuclearization of the Korean peninsula, and President Trump reiterated his intention to meet with North Korean leader Kim Jong Un by the end of May," the White House said.
"The two leaders expressed cautious optimism over recent developments and emphasized that a brighter future is available for North Korea, if it chooses the correct path."
Before a date or a venue for the summit can be set, North Korea will have to publicly confirm that it sent the invitation and intends to honor it, by attending a meeting to discuss giving up its nuclear arsenal.
There had been speculation that Pyongyang might do so Friday, when Ri Yong Ho met Swedish Prime Minister Stefan Lofven and Foreign Minister Margot Wallstrom, but afterwards Swedish officials said the talks would be extended into Saturday.
Sweden has longstanding ties with North Korea. Its diplomatic mission in Pyongyang, which opened in 1975, was the first Western embassy established in the isolationist country and now represents US, Canadian and Australian diplomatic interests, with Sweden playing a key liaison role.
Ri and Wallstrom dined at the foreign ministry on Thursday evening, then met again on Friday at Villa Bonnier, a lavish building near the US embassy used by the government for official functions.
"It was a good and constructive atmosphere. We'll see what happens next," Wallstrom told reporters after Friday's talks.
Ri made no comment as he left.
- Nuclear standoff -
"If we can use our contacts in the best way, we will do so," Wallstrom said, noting the situation on the Korean peninsula was "of interest to us all."
Ri's delegation included Choe Kang Il, deputy director general of the foreign ministry's North America section.
Some media have reported that Ri, who was stationed at North Korea's embassy in Stockholm from 1985 to 1988, will stay in the Scandinavian country until Sunday, though Swedish officials would not confirm this.
A senior US administration official told AFP: "No US government staff are meeting with the North Koreans in Sweden."
- 'Serve as facilitator' -
International media have speculated that Sweden could either help set up a summit or be a potential location if a tete-a-tete were to be confirmed. The foreign ministry has refused to comment
Speaking in Berlin on Friday, Lofven said that if Sweden "can serve as a facilitator to bring about results, then we will of course do that."
Japanese broadcaster TBS said Japan's Prime Minister Shinzo Abe and Moon discussed North Korea in a telephone call on Friday.
TBS said Abe told Moon he wanted North Korea to not only suspend nuclear and missile testing, but also accept International Atomic Energy Inspectors on its soil.
Kono asked Vice-President Mike Pence to ensure that the decades-old issue of Japanese nationals abducted by North Korea would be raised -- along with the nuclear and missile issue -- in any summit between Trump and Kim, Kyodo news agency reported.
Some reports have suggested that Japan is less optimistic than its allies in Seoul and Washington that the talks are a good idea, but US officials said talks with both Kono and Kang at the State Department had gone well.
"Both sides agreed that the announcement of a meeting between President Trump and North Korean leader Kim Jong Un is an historic opportunity and that the global maximum pressure campaign is working and must remain in effect," spokeswoman Heather Nauert said.