SEOUL - SOUTH Korea will demand the release of a citizen held by North Korea when the two countries meet for a third round of talks over the fate of a troubled joint factory park, an official said Thursday.

Friday's meeting at the North Korean border town of Kaesong, the site of the industrial park, comes amid rising tension in the peninsula over the North's nuclear programme. Pyongyang last week vowed to bolster its nuclear programmes and threatened war in protest of UN sanctions taken for its May 25 nuclear test.

'I think the government believes the most important thing is the issue of the detained worker and safeguarding (his) safety,' Unification Ministry spokesman Lee Jong-joo told reporters.

Ties between the two Koreas have deteriorated since conservative President Lee Myung-bak took office in Seoul in February last year.

His hard-line policies prompted the North to cut off ties with the South and halt all key joint projects except for the South Korean-run complex at Kaesong.

But the complex also faces trouble because North Korea has restricted border traffic, stranding hundreds of South Korean workers several times. South Korean companies in Kaesong also complain that the North's nuclear program is affecting their business - their buyers are canceling orders because of the political climate.

The two Koreas met the first time in April and again last Thursday to talk about the future of Kaesong. At the last meeting, North Korea demanded a 3,000 per cent increase in rent for the site and a fourfold hike in wages for the 40,000 North Korean workers employed there.

Further straining ties is the issue of a South Korean worker at the complex who has been detained since late March for allegedly denouncing Pyongyang's political system. The North has repeatedly rejected Seoul's demand for his release.

'This matter should be discussed together with the other issues that North Korea has raised about the Kaesong complex,' Ms Lee, the ministry spokeswoman, said.

On Tuesday, President Lee also urged the North to immediately free the worker without any conditions. Lee, who was speaking in Washington, warned that the international community would not tolerate such a 'reckless detention' of the South Korean worker and two other detained US journalists. -- AP