SEOUL -- U.S. and North Korean officials sought to bridge their differences on denuclearization and sanctions during three days of talks ended Monday, with Yonhap News Agency citing an "intensive discussion" ahead of a second summit between the countries.

Stephen Biegun, the U.S. special representative for North Korea, met with North Korean Vice Foreign Minister Choe Son Hui at a recreational facility outside of Stockholm, according to the South Korean news agency.

The American side discussed details of a recent meeting between President Donald Trump and Kim Yong Chol, North Korea's lead negotiator for nuclear talks, and covered potential steps by both sides, Yonhap said. Trump and North Korean leader Kim Jong Un are expected to meet in February.

Washington intends to maintain pressure and economic sanctions on Pyongyang until it carries out a complete denuclearization. But the North has insisted on a "gradual and simultaneous" approach in which both sides take small steps, including an easing of sanctions. The working-level officials were expected to explore terms acceptable to both sides in order to yield results at the Trump-Kim summit.

"Constructive talks have been held covering issues concerning developments on the Korean peninsula, including confidence building, economic development and long-term engagement," said a spokesman for Sweden's foreign ministry.

Pyongyang was expected to ask the U.S. to condone economic cooperation between North and South Korea in exchange for dismantling its Yongbyon nuclear facility and a portion of its intercontinental ballistic missile fleet.

In an apparent nudge to Seoul, North Korea's state-owned Uriminzokkiri propaganda website on Monday cited the importance of the South's stance on resuming two projects -- the jointly operated Kaesong Industrial Park and tourism at Mount Kumgang in the North -- tied to inter-Korean reconciliation and cooperation.

South Korea's Lee Do-hoon, special representative for Korean Peninsula peace and security affairs, may have joined the negotiations in Sweden. Japan's Foreign Ministry sent Kenji Kanasugi, director-general of the Asian and Oceanian Affairs Bureau.

One preparatory meeting was not enough for the first Trump-Kim summit in June 2018.

U.S. Secretary of State Mike Pompeo spoke Monday by phone separately with the South Korean and Japanese foreign ministers, confirming coordination on the February summit.