"The road ahead of us could be bumpy and might have more ups and downs than the road we have gone through so far," Lim Sung-nam, the chief South Korean delegate, said in his opening remarks on Monday.
The two-day meeting is being held under the auspices of the six-nation talks on North Korea's nuclear weapons program, which also include South Korea, China, Russia and Japan.
"The road ahead of us could be bumpy"
Lim Sung-nam, chief South Korean delegate
Under the terms of a Chinese-brokered agreement, North Korea agreed to disable its main nuclear facilities and declare all its weapons programs by year's end.
In return the other five parties to the deal agreed to provide energy aid to the impoverished North, as well as other political and diplomatic benefits.
North Korea has already shut down its sole operating reactor at Yongbyon under the initial phase of the deal in return for an initial shipment of 50,000 tons of fuel oil.
Monday's talks in Panmunjom came as a European envoy returning from a visit to the North said he was convinced that Pyongyang was prepared to fulfil all its promises.
"I think there is really now a big chance, a window of opportunity, and I do expect that they will fulfil from the North Korean side what they have promised,'' said Hubert Pirker, who led a delegation of EU parliamentarians on a week-long visit to the North.
Speaking after crossing the border back into South Korea, Pirker said that North Korea was also eager to increase contacts with the outside world, both at an official level and for training.