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.
Some Swedish and foreign media have said that Ri - who was stationed at North Korea's embassy in Stockholm in 1985-1988 - will stay in the Scandinavian country until Sunday for other talks, though Swedish officials would not confirm those reports.
Sweden has had diplomatic relations with North Korea since 1973, and is one of the few Western countries to have an embassy in Pyongyang.
North Korean Foreign Minister Ri Yong-Ho and his delegation arrive at Arlanda airport outside Stockholm, Sweden. Wallstrom spokesman Pezhman Fivrin said Friday that the talks had been extended by a day, without elaborating.
Ri Yong Ho held talks in Stockholm with Swedish Prime Minister Stefan Lofven and Foreign Minister Margot Wallstrom a week after the US President agreed to a historic summit with the North Korean leader.
Merkel commented on the poisoning of former Russian spy
She's been urged to be tougher and hurt Russian Federation where it counts - in the pockets of its millionaires and billionaires. She also said that she wanted to freeze Moscow's assets in the United Kingdom , but provided no further details.
The historically neutral European country, whose embassy represents United States interests in the North Korean capital, has often played the role of intermediary in discussions between Washington and Pyongyang.
"We've made a decision to narrow down the agenda topics to denuclearizing the Korean peninsula, securing permanent peace to ease military tension and new, bold ways to take inter-Korean relations forward", Im, the head of South Korea's summit preparation team, told reporters.
"We have always said we want to be a mediator that facilitates this process", he said.
Im added Moon may meet Trump after the inter-Korean summit but before Trump's planned summit with Kim in May.
There was no official word from North Korea since the invitation was delivered via South Korean officials in Washington.
"We are a country that is militarily non-aligned and have a longstanding presence in North Korea, and with the trust we enjoy we think we can play a role".
The diplomatic wheels started turning rapidly at the beginning of the year when the two Koreas worked to bring a handful of athletes from the North to compete in the Winter Olympics in South Korea.