South Korea says some North Korean officials have returned to an inter-Korean liaison office three days after the North abruptly withdrew its entire staff citing unspecified instructions from "higher-level authorities."

Seoul's Unification Ministry says four to five North Korean officials showed up for work Monday at the liaison office in the North Korean border town of Kaesong.

It wasn't immediately clear why North Korea sent some workers back to the office or whether it will restore a full staff.

The North's decision to withdraw its staff came a week after its vice foreign minister threatened to pull out of nuclear negotiations with the United States following the collapse of a nuclear summit between leader Kim Jong Un and President Donald Trump.