FILE PHOTO - South Korean President Moon Jae-in and North Korean leader Kim Jong Un walk during a luncheon, in this photo released by North Korea's Korean Central News Agency (KCNA) on September 21, 2018. KCNA via REUTERS

SEOUL (Reuters) - South and North Korea will launch a field study on Friday to relink railways cut since the 1950-53 Korean conflict, Seoul’s Unification Ministry said on Wednesday, the latest development in improving ties between two sides technically still at war.

The announcement came after the U.N. Security Council granted sanctions exemptions last week following consultations between South Korea and the United States.

The survey would be a first step in an agreement to reconnect rail and road links reached by South Korean President Moon Jae-in and North Korean leader Kim Jong Un at their first summit in April.

About 30 officials from each side are expected to take part in the 18-day study, which will include a 2,600-km (1,615-mile) train trip. They will inspect two routes in North Korea, between Kaesong and Sinuiju in the west and Mount Kumgang and the Tumen River in the east, which would ultimately be linked to the South, the ministry said.

“After the joint survey, we will work on drawing up a basic framework for the project, additional research and design, and the actual construction would be conducted in line with progress on North Korea’s denuclearization,” the ministry said in a statement.

U.S. officials have been concerned that inter-Korean relations may be advancing too fast even as Pyongyang and Washington struggle to make headway in denuclearization talks.

North and South Korea are technically still at war because the 1950-53 conflict ended in a truce, not a peace treaty.

North Korea has for years pursued nuclear and missile programs in defiance of U.N. sanctions. But the two Koreas moved to defrost relations this year.

Kim and U.S. President Donald Trump pledged to work toward denuclearization at their landmark June summit in Singapore, but the agreement was short on specifics.