COPENHAGEN, Denmark (AP) — Talks between American, South Korean and North Korean diplomats in Sweden — considered a preparation for an upcoming U.S.-Korea summit, have ended, an official with the independent think tank that co-hosted the meeting said Tuesday.

Stephanie Blenckner of the Stockholm International Peace Research Institute, or SIPRI, that focuses on research on conflicts, armaments and arms control, said the talks ended Monday evening. She gave no details.

Blenckner said Tuesday SIPRI "found the meeting constructive."

Talks focused on the security situation on the Korean Peninsula and "confidence-building" relations, Foreign Ministry spokesman Erik Karlsson said, declining to elaborate.

Foreign Minister Margot Wallstrom said Monday experts in nuclear disarmament, economic development and regional security attended the diplomats' meeting in Sweden.

The "small format" talks, as described by the Swedish Foreign Ministry, included North Korean Deputy Foreign Minister Choe Son Hui, Lee Do-hoon of South Korea and Steve Biegun, U.S. special envoy for North Korea negotiations, plus diplomats from Sweden.

Authorities haven't disclosed the venue or schedule for the talks taking place before a meeting between U.S. President Donald Trump and North Korean leader Kim Jong Un, expected in late February.

The first meeting ever to bring the leaders of North Korea and the U.S. face-to-face took place in June when Kim and Trump met in Singapore.