North Korea and the U.S. ended their working-level talks in Sweden on Monday to prepare for a second summit between their leaders.

According Reuters, a spokesman of Sweden's Foreign Ministry said constructive talks have been held covering issues concerning developments on the Korean Peninsula, including confidence building, economic development and long-term engagement.

U.S. Special Representative Stephen Biegun and his North Korean counterpart Choe Son-hui held three days of discussions at a remote facility just outside Stockholm.

South Korea's chief nuclear envoy Lee Do-hoon also stayed at the facility for bilateral or trilateral talks to serve as a mediator. 

Through the talks, the participants reportedly had extensive and candid discussions on issues related to the second U.S.-North Korea summit, especially the North's denuclearization and the U.S.’ corresponding measures.  

Biegun reportedly left the facility at 10:45 a.m. Monday, and Choe and Lee were seen leaving two hours later. The South and North Korean envoys are thought to have held talks during the two hours.