The two Koreas continued their seventh general-level military talks into a second day at the truce village of Panmunjeom.
On Thursday, they are discussing the location of a joint fishing zone in the West Sea.
A plenary session in which each side reaffirmed its stance was immediately followed by working-level discussions.
The South wants the Northern Limit Line as the reference line, with each side sharing the same amount of area. The North wants the zone below the NLL, setting the stage for tough talks.
Earlier in the day, the two Koreas adopted an agreement on military guarantees that would affect the Gaesong Industrial Complex and the Mount Geumgang tourist zone. The accord expanded transit times allowed for both sides and paved the way for Internet and fixed and wireless phone services at the two inter-Korean sites.
The agreement took effect after being signed by the defense chiefs of the two countries the same morning.