North Korea on Friday refused to entertain an official request from Seoul to release a South Korean missionary arrested four months ago on espionage charges.
The South's Unification Ministry said it had attempted to send a written demand for Kim Jeong-Wook's immediate release through the border truce village of Panmunjom.
But North Korean officials refused to accept the message, the ministry said.
At a government-arranged news conference in Pyongyang on Thursday, Kim, 50, said he had been engaged in a number of "anti-government" activities that he had undertaken with the support of South Korea's intelligence agency.
Foreigners arrested in North Korea are often required to make a public "confession" which can then expedite their eventual release.
Seoul dismissed the charges against Kim, saying he was involved in "purely religious activities."
Fellow activists and missionaries said Kim had been providing shelter and food for seven years to North Korean refugees living in China's northeastern border city of Dandong.
They said he had crossed the Yalu border river in October to establish the whereabouts of some North Korean refugees who had been arrested in Dandong by Chinese authorities and repatriated.
Although religious freedom is enshrined in the North Korean constitution, it does not exist in practice and religious activity is severely restricted to officially-recognised groups linked to the government.
Last week North Korea arrested an Australian missionary, John Short, 75, after he left a Christian pamphlet in a Buddhist temple.
US citizen Kenneth Bae, described by a North Korean court as a militant Christian evangelist, was sentenced last year to 15 year's hard labour on charges of seeking to topple the government.
hollywoodtone.blogspot.com N. Korea snubs South request on detained missionary