South Korea on Thursday offered North Korea formal talks to resolve the suspended operations at their joint Kaesong industrial zone, and warned of "grave action" if Pyongyang declines.
"We officially propose talks between government authorities," Unification Ministry Spokesman Kim Hyung-Seok said, adding that Pyongyang should reply to the offer by Friday.
"If North Korea rejects these proposed official talks, we would have to take grave action," Kim said, without elaborating.
The warning appeared to hint that South Korea was considering a permanent withdrawal from the zone, which normally employs 53,000 workers at 123 South Korean companies.
North Korea has blocked South Korean access to Kaesong since April 3, amid soaring military tensions on the Korean peninsula.
On April 9, it pulled out its entire workforce and suspended operations in the zone, which lies 10 kilometres (six miles) inside North Korea and was established in 2004 as a rare symbol of inter-Korean cooperation.
There are currently 176 South Korean staff still in Kaesong, compared with the normal number of around 850.
The North's decision to suspend operations was unexpected.
Neither of the Koreas has allowed previous crises to significantly affect the complex, a valued source of hard currency for the impoverished North and seen as a bellwether of stability on the Korean peninsula.