North Korea's foreign minister is in Sweden for a surprise visit, ahead of a possible meeting between US President Donald Trump and Kim Jong-un.
Pyongyang said Ri Yong-ho's trip was for "bilateral relations and issues of mutual concern".
Sweden has a long history of mediating between Washington and Pyongyang.
So the visit has prompted speculation it might be part of preparations for the US-North Korea summit.
Donald Trump last week accepted an invitation for direct talks with Mr Kim, a shock announcement from the two leaders who have traded threats and insults for months.
There has been no official word from North Korea since the invitation was delivered via South Korean officials in Washington.
Swedish Prime Minister Stefan Lofven told his country's news agency TT that "if the main actors want Sweden to play a role then we are ready to do that".
"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. But it has to be the main actors who decide which role Sweden will play."
The US said it was aware of the meeting in Stockholm, but did not know whether it was related to any US-North Korean talks.
The plans for the meeting between Mr Trump and the North Korean leader took the world by surprise last Friday.
It followed a year of heated rhetoric between North Korea and the US, and growing global concern that the hostilities might escalate into military confrontation.
In the invitation relayed by South Korean officials, Mr Kim said he was "committed to denuclearisation".
However uncertainty remains over what would be a landmark summit. It is not yet clear:
where the talks will take place. North Korea and the US are considered unlikely. More likely places are the border between the two Koreas China, a neutral country - like Sweden - or international waters
what North Korea wants in exchange for the meeting and for promising denuclearization
whether the offer from Pyongyang is serious or just intended as a propaganda boost
whether the summit will ultimately take place at all
Sweden has had longstanding ties with North Korea and its embassy in Pyongyang was one of the first Western diplomatic missions in North Korea in the 1970s.
As the US has no embassy in North Korea, Sweden has in the past acted as its diplomatic representative in the authoritarian state.
Sweden, which is not a NATO member, has for instance helped with the release of US citizens held by the North.