South Korea's point man on North Korea Wednesday urged the communist state to drop its hard-line tactics, saying they would only undermine ties.

"North Korea's hard-lined measures can no longer serve as (viable) strategies or tactics," Unification Minister Hyun In-Taek told an annual meeting of government officials and advocates of unification with the North.

"Confrontation and discord will benefit neither the North nor the South," he said, adding South Korea would patiently expand cooperation with North Korea.

The two sides must open sincere dialogue to discuss all pending issues, including the North's nuclear programme, "with open hearts," he said, quoted by Yonhap news agency.

Diplomatic efforts are intensifying to revive six-nation nuclear disarmament negotiations which the North abandoned last April, a month before it staged a second nuclear test.

Before it returns to dialogue, the North is calling for UN sanctions to be lifted. It also wants a US commitment to discuss a peace pact to replace the armistice which ended the 1950-1953 Korean War.

The North warned Tuesday that South Korean-US war games this month would torpedo efforts to rid the peninsula of nuclear weapons, and vowed to strengthen its atomic arsenal if necessary.

The North's military last week accused South Korean and US troops of planning a surprise attack under the pretext of the exercise and warned it could respond with atomic weapons.

The North has also announced it is holding four South Koreans for illegal entry but has given no details. A South Korean activist has said they entered the North from China.