South Korea is warning Pyongyang to uphold the human rights of South Koreans working at a joint industrial facility in the North.  The South's main policymaker on North Korea warns the North's prolonged detention of an executive from the South could impact the future of the cooperative zone. 

South Korean Unification Minister Hyun In-taek said Tuesday North Korea's detention of a South Korean businessman is an "essential problem" in managing a joint industrial park near the North Korean city, Kaesong.

Hyun told international reporters in Seoul the North had not allowed South Korea to see or talk to the executive since he was taken into custody, last month.  He has also been denied any form of legal representation from the South.

"North Korea must understand the seriousness of this issue and show a positive attitude for its resolution," said Hyun.

The man in custody, known for now by his surname "Yu," is an employee of South Korea's Hyundai Asan, the corporation that manages two inter-Korean cooperation zones in the North.  Smaller South Korean companies invested in the Kaesong zone use about 38,000 North Korean workers for inexpensive labor, manufacturing items like housewares and apparel. 

South Korean officials say Yu is accused of making disparaging comments about the North's political system and possibly encouraging a North Korean woman to defect.

Minister Hyun says the way Yu's case is handled will have very important consequences for the future stable development of the Kaesong zone.

"The personal safety of our workers in Kaesong must be guaranteed," he said.

The erosion of trust in the Kaesong zone mirrors the steady worsening of North-South relations since conservative South Korean President Lee Myung-bak was inaugurated, last year.

Mr. Lee ended a ten-year policy of uncritically transferring billions of dollars in South Korean public funds to the North, with the aim of creating mutual trust.  The Lee administration says such investments must be reciprocated by efforts in Pyongyang to eliminate the country's nuclear weapons arsenal.

North Korea has responded by calling Mr. Lee a "traitor" and grinding the pace of cross-border activity to a near halt.

In last week's first government meeting between the two sides in a year, North Korea refused to discuss the Kaesong detention, instead demanding higher salaries and rental fees from the South.   South Korea pays about $75 a month for every North Korean worker.  However, the money goes straight to the North Korean state and it is unclear how much actual income the workers receive.

Hyun says he agrees with economists that Kaesong fees should be kept low.

He says, if wage or land use costs go too high, Kaesong's competitiveness will be reduced because of other cheap labor sources like China and Vietnam.

Hyun says South Korea is studying the North's proposal and will present a response at talks expected, to be held soon.