North Korea pledged to shut down its main nuclear reactor within 60 days in exchange for energy aid.
Pyongyang has already invited the chief UN nuclear inspector to visit to discuss verification of a shutdown of the reactor.
South Korea plans to focus this week's cabinet-level talks in Pyongyang on winning a firmer North Korean commitment to carry out the nuclear deal and on measures aimed at bringing permanent peace to their divided peninsula.
Lee Jae-joung, the chief South Korean delegate and unification minister, praised the nuclear deal during an informal meeting with Kwon Ho Ung, his North Korean counterpart and senior cabinet councillor.
"A good agreement was reached ... based on the principle of equality and balance," Lee told Kwon.
Kwon did not respond to the comment, the reports said.
Later in the day, Lee told a welcoming dinner hosted by Pak Pong Ju, the North Korean prime minister, that the two Koreas should get reconciliation projects back on track now that the "skein of thread that gave us a hard time last year" is being unwound, referring to the nuclear standoff.
In Seoul, Roh Moo-hyun, South Korea's president, said it was important to show North Korea that it would get more for abandoning its nuclear weapons than keeping them.
"We have to keep sending signals that their security will be guaranteed and they could get profits through reform and openness," Roh told a news conference.
Roh also said he believed North Korea would not use its nuclear weapons unless attacked first, saying it would be something "only mental patients can do".
The cabinet-level contacts, which began after the two Koreas' only summit in 2000, are the highest regular dialogue channel between the two rival states that are still technically at war because the 1950-53 Korean war ended in a ceasefire, not a peace treaty.
The talks, in their 20th session, have often been overshadowed by political tensions, especially over North Korea's missile and nuclear programmes.
North Korea abruptly pulled out of talks in July over the South's refusal to offer aid after the North test-fired missiles. Their relations further soured after North Korea's nuclear test on October 9, 2006.
North Korea is expected this week to renew its demand for fertiliser and rice aid. The South is widely believed to be willing to resume such shipments, but remains unclear on how much it will give.
Other topics expected to be on the agenda include a resumption of reunions of families split by the armed border, and tests of a train line that crosses the frontier.
The reunions have been on hold since South Korea suspended aid last year, and a planned test of the train line was cancelled last year because North Korea's military said proper security arrangements had not been made.