North Korea and the United States are known to have held a working-level meeting at the inter-Korean border last weekend where they discussed the North’s follow-up measures over its denuclearization as well as a declaration to formally end the Korean War. 

A diplomatic source said on Tuesday that the two sides exchanged various opinions, but appear to have entered a concrete phase of discussions through the working-level meeting held at the truce village of Panmunjeom. 

It's known they will hold more meetings at the same venue this weekend. The source said there are more communication channels between the North and the U.S. than is publicly known. 

South Korea’s presidential adviser Moon Chung-in told Yonhap News that there's a high possibility U.S. Secretary of State Mike Pompeo will make his fourth visit to Pyongyang this month to break the impasse in the Pyongyang-Washington negotiations over the North’s denuclearization.