South Korea warned Thursday it will take "necessary steps" if Pyongyang continues its unauthorised use of a joint industrial complex in the North once seen as a symbol of reconciliation.
More than 50,000 North Korean workers once worked at the Kaesong Industrial Complex, churning out products ranging from watches to clothes for about 125 South Korean companies that supplied the funding and equipment.
Seoul pulled out of the venture -- launched in the wake of the 2000 inter-Korean summit -- in 2016 in response to a nuclear test and missile launches by the North, saying Kaesong profits were helping fund the provocations.
But the North has continued using the facility and its South Korean-owned assets without permission, Seoul's unification ministry said Thursday.
South Korea's liaison office sent a notice on Thursday demanding activity at the factory complex cease, but North Korea refused to accept it, the ministry said.
The announcement came a day after North Korea's Rodong Sinmun newspaper released a set of photographs showing what appeared to be a South Korean bus once used to carry workers to the complex running in Pyongyang.
The continued operation of the facilities "regardless of the will of the businessmen is a clear violation of property rights" and the two Koreas' agreement on investment guarantees, Seoul's notice said, according to the ministry.
"North Korea should stop this immediately. If there is no corresponding response from North Korea regarding our request, we will take necessary steps assuming that North Korea has admitted to operating the complex without permission," the notice said.
What action might be taken was not specified.
While open, the business park was virtually the last remaining form of economic cooperation between the Koreas, providing precious hard currency for the impoverished North and cheap labour and tax breaks for the involved companies.
North Korea has doubled down on the expansion of its military arsenal and nuclear programme since a 2019 Hanoi summit between leader Kim Jong Un and then-US president Donald Trump failed to yield any meaningful outcome.
In recent weeks, it has tested what state media has claimed was an underwater, nuclear-capable drone and carried out the launch of an intercontinental ballistic missile.
Officials in Seoul and Washington have warned since early 2022 that North Korea may be preparing to conduct its seventh nuclear test, with some experts saying it could be imminent.