SEOUL, South Korea — North Korea said on Saturday that it will allow journalists from the United States and other countries to witness the shutting down of its underground nuclear test site between May 23 and 25, which will be done by collapsing all its tunnels in a controlled explosion and sealing their entrances.

North Korea decided last month to end all nuclear and long-range ballistic missile tests and close its only known nuclear test site, located in Punggye-ri in the northeast of the country. When the leader of North Korea, Kim Jong-un, met with South Korea’s president, Moon Jae-in, on April 27, he promised to invite outside journalists and experts this month to watch the dismantling of the test site, Mr. Moon’s office said.

Mr. Kim promised these confidence-building steps as he has tried to improve ties with Washington ahead of his planned summit meeting with President Trump in Singapore on June 12. Mr. Kim also met with Secretary of State Mike Pompeo this week in Pyongyang, the North Korean capital, and let him take three American prisoners home with him.