Senior officials of North Korea and the U.S. are holding working-level talks in Sweden to prepare for a second summit between their leaders. 

Stephen Biegun, Washington's special representative for North Korea, and North Korean Vice Foreign Minister Choe Son-hui will reportedly continue talks for the third day on Monday at a remote facility near Stockholm. 

Staying together at the facility which is under tight security, the two sides are said to be in intensive discussions on the North's denuclearization and the U.S.' corresponding measures. 

South Korea's top nuclear envoy Lee Do-hoon, who arrived in Sweden on Friday, is reportedly joining the talks or holding separate talks with the two parties, when necessary, to serve as a mediator. 

Negotiations on most key issues are likely to wrap up on Monday.