Vehicles carrying South Korean officials of the inter-Korean liaison office in North Korea head to Gaesong through the inter-Korean customs, immigration and quarantine office on Gyeongui Line in Paju, Gyeonggi Province, Monday. Yonhap

Dozens of South Korean officials headed to an inter-Korean liaison office in North Korea on Monday, the unification ministry said, despite Pyongyang's abrupt pullout of its staff from the office last week.

Around 40 South Korean officials crossed the western land border on their way to the liaison office in the North's border town of Gaesong, according to the ministry. Together with about two dozen people already there, about 60-70 South Korean officials are expected to staff the office this week, officials said.

Their dispatch came despite the North's withdrawal of its staff from the office Friday.

The North did not give a clear reason for the pullout, only saying the decision was based on an order from "higher-ups." Experts and analysts said the move appears to be designed to pressure Seoul to do more to persuade the United States to lower its demands in the stalled denuclearization negotiations.