The inter-Korean liaison office in Kaesong on September 14, 2018. (Photo: Yonhap/ VNA)

The office in the Northern city of Kaesong was opened in September as North and South Korea began establishing closer ties, but the North pulled its stake last week amid a deadlock in talks between Washington and Pyongyang.

South Korea’s unification ministry said some of the North Korean staff were back at work on Monday saying they had come to cover their "shift as usual". It said the North did not offer details as to why they had returned or pulled out in the first place.