Senior officials from North Korea and the United States reportedly kicked off working-level talks on Saturday in Sweden to prepare for a second summit between their leaders.

Stephen Biegun, Washington's special representative for North Korea, arrived in Stockholm on Saturday afternoon for four days of talks with North Korean Vice Foreign Minister Choe Son-hui at a remote facility outside of Sweden's capital.

It is the first time that Biegun has met Choe for working-level denuclearization talks since he became the U.S. nuclear envoy in August last year.

South Korea's top nuclear envoy, Lee Do-hoon, also arrived in Sweden on Friday for possible three-way negotiations with them as a potential mediator in denuclearization talks.

The officials from the three nations are expected to explain their respective positions and seek to produce agreements regarding the second summit through three-way or bilateral talks between the two Koreas or between North Korea and the United States for four days until next Tuesday.

The secret talks came as Kim Yong-chol, a top North Korean official, wrapped up his three-day visit to Washington on Sunday after meeting with U.S. President Donald Trump and agreeing to hold a second summit next month between Trump and the North's leader, Kim Jong-un.