A British-run travel agency which specialises in tours to North Korea disclosed Monday that South Korea was blocking its website because of alleged pro-Pyongyang material.

Beijing-based Koryo Tours described the ban as "disproportionate and unjust". But a Seoul official said the action, in force since late January, would continue until changes were made in its content.

Koryo Tours has been promoting tourism and cultural exchanges with North Korea since 1993.

It said Seoul had blocked access on South Korean servers to its company website, with the addresses www.koryogroup.com and www.koryotours.com, at the request of the National Intelligence Service (NIS).

This was on the grounds that the content violated the South's National Security Act and other laws banning "propagandist" information about the North.

The tour company said in a statement its site was also seen as breaching a law banning South Koreans from contacting or visiting the North without permission.

Koryo Tours said it changed some pictures and removed links to certain North Korean websites at the request of the Korea Communications Standards Commission.

"But we are not prepared to delete large amounts of factual content," it said.

"We believe that the blocking of our website is disproportionate and unjust."

The company said its website did not encourage South Koreans to visit the North. "Our company has no political agenda and only seeks to raise awareness and mutual understanding between North Korea and the rest of the world."

The Korea Communications Standards Commission confirmed the site was blocked at the request of security authorities including the NIS.

"Our move will be maintained until Koryo Tours revises its website to reflect our recommendations," a commission official told AFP on condition of anonymity.

"There have been some changes at our request, but we still believe such changes are insufficient. Some of its content is against our security law and propagates North Korea's political system and ideology."