Updated

North Korea and South Korea made no significant progress in talks concluding Thursday on their joint industrial park, which has been one of the most prominent symbols of cooperation amid tensions between the neighbors.

The two sides held meetings starting Tuesday in the North's border city of Kaesong to assess their joint tours in December of industrial parks in China and Vietnam, and to discuss ways to further develop their own complex at Kaesong.

The meeting also was aimed at setting an agenda for working-level talks, but no significant progress was made as Seoul balked at North Korea's demands that the issue of wage hikes should be included, Unification Ministry spokesman Chun Hae-sung said. The two sides also failed to set a date for the next round of talks, he said.

The Kaesong complex is a key element of inter-Korean cooperation. About 110 South Korean factories employ some 42,000 North Korean workers, providing the impoverished country with a key legitimate source of hard currency.

The South Korean delegation returned home Thursday, one day behind schedule.

This week's meeting came amid fresh tensions on the divided peninsula over the North's threat to break off dialogue and attack Seoul in response to its reported contingency plan to handle any unrest in the North.

Unrest in North Korea is a distinct possibility in coming years, the Korea Institute for National Unification said in a report posted on its Web site late Tuesday.

The state-run think tank predicted a military coup, popular uprising, a massacre or mass defections after North Korean leader Kim Jong Il dies. Kim, who turns 68 next month, is believed to have suffered a stroke in 2008.

Kim probably won't survive past 2012, the think tank said — though it cited no evidence for its speculation. His death could touch off a military coup or power struggle unless he manages to stabilize succession plans soon, the report said.

Kim is believed to be grooming his youngest son to take over as leader of the nation of 24 million.

The think tank also speculated that Kim could delegate much of his authority to brother-in-law Jang Song Thaek, a member of the all-powerful National Defense Commission, until the son — now in his 20s — is able to take power.

The North Korean leader himself succeeded his father, Kim Il Sung, in 1994 in communism's first hereditary transfer of power. The institute also said a collective leadership, or another figure, could emerge to rule the country after Kim's demise.

Meanwhile, South Korea's Defense Minister Kim Tae-young called for a pre-emptive strike on North Korea if there is a clear indication the country is preparing a nuclear attack. His comments Wednesday echoed similar remarks he made in 2008, when he was chairman of South Korea's Joint Chiefs of Staff, which prompted the North to threaten to destroy the South.

Envoys from neighboring nations are seeking to convince North Korea to return to nuclear disarmament negotiations.

Pyongyang quit six-nation disarmament talks involving China, Japan, Russia, South Korea and the United States in anger over international condemnation of a long-range rocket launch last April. The regime carried out an underground nuclear test the following month in defiance.

North Korea has shown some willingness to return to the talks, but recently demanded that sanctions be lifted first. The North also called for a peace treaty to formally end the 1950-53 Korean War, saying the agreement would help end hostile relations with the U.S. and promote the denuclearization of the Korean peninsula.

The U.S. has rejected the demands for a peace treaty or a lifting of sanctions.