SEOUL, South Korea — The United Nations Security Council has approved a plan by North and South Korea to conduct a joint field study on connecting their railways, exempting the project from the extensive sanctions the U.N. has imposed on the North over its nuclear weapons program, officials said on Saturday.

During his three summit meetings this year with the North’s leader, Kim Jong-un, President Moon Jae-in of South Korea has offered to help renovate North Korea’s decrepit railway system and link it with the South’s, dangling the project as one of the biggest economic benefits the North could expect should it denuclearize.

To whet the North’s appetite, South Korea offered to send a train and engineers across the border to conduct a joint field study on the conditions of the North Korean rail system. North Korea quickly accepted.

But plans to conduct the study were thwarted in August, and again last month, because of American concerns that it might violate United Nations sanctions, which include severe limits on shipments of fuel and other goods to the North. South Korea would have to bring fuel and equipment into the North to conduct the study.