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.

Foreign Minister Margot Wallstrom held discussions with counterpart Ri Yong Ho on Thursday and Friday. Ri also met with Swedish Prime Minister Stefan Lofven.

"The meetings are continuing today (Saturday)," Wallstrom's spokesman Erik Wirkensjo told AFP.

AFP journalists saw Ri arriving at the Swedish foreign ministry. As in the previous days, he did not make any comments to the media.

The North Korean minister also visited the Stockholm International Peace Research Institute global security think tank and met with chairman Jan Eliasson and other senior officials to discuss the situation in the Korean peninsula, a statement said.

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.

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 honour it, by attending a meeting to discuss giving up its nuclear arsenal.