South Korea appealed to North Korea to scrap its nuclear weapons program, but got no response Sunday on the first of three days of talks.
The talks in the North Korean capital of Pyongyang originally were to focus on reconciliation between the two nations on the divided peninsula.
But South Korea devoted most of its keynote speech to persuading the North that its nuclear weapons program violates a 1994 agreement with the United States and should be halted.
"We demanded that North Korea faithfully honor all international agreements it has signed," Rhee Bong-jo, a South Korean spokesman, said after the first round of talks.
North Korea did not respond, but officials cautioned their counterparts from the south "not to be too pessimistic" about prospects for agreements between the two nations.
The North's chief delegate, Kim Ryong Song, even predicted "good results" from the talks, according to pool reports distributed in Seoul, the South's capital.
South Korean officials said they hoped to hear a North Korean response during another round of talks Monday.
The talks, the eighth in a series since a historic inter-Korean summit in 2000, were scheduled to continue until Tuesday.
"Overall, the atmosphere of the talks was heavy, but sincere," Rhee said. He also said other issues taken up included a proposal to account for thousands of people missing during and after the 1950-53 Korean War.
During talks with visiting U.S. Assistant Secretary of State James Kelly in Pyongyang on Oct. 3-5, North Korean officials acknowledged they had a uranium-enriching program to make weapons.
The program violates a 1994 agreement for energy-starved North Korea to abandon its suspected nuclear weapons program in exchange for two modern, light-water nuclear reactors and 500,000 tons of fuel oil a year until the reactors are completed.
During the talks with Kelly, North Korean officials said they considered the 1994 agreement invalid because the reactors were not expected to be finished by 2003 as promised. The project has been delayed by funding problems and tension on the Korean Peninsula.
Kelly was in Japan on Sunday for talks with Japanese leaders about North Korea's nuclear program. He was expected to discuss temporarily freezing construction on the reactors in North Korea.
A U.S. State Department official told The Associated Press Saturday night that no decision has been reached yet on the 1994 accord. The official, speaking on condition of anonymity, said the United States wants to consult with its allies before making a decision on the pact.
In an editorial Sunday, a North Korean newspaper accused the United States of plotting to conquer its adversaries in the name of its war on terrorism.
"By escalating the war, the U.S. seeks to threaten and militarily contain those countries which stand opposed to it," the state-run Rodong Sinmun said.