Greenpeace on Monday accused South Korea of seeking to "silence" opposition to its nuclear energy programme after two of its campaigners were barred from entering the country.
The environmental group said the two senior campaigners — Jan Beranek and Rianne Teule — were stopped by immigration officials at Incheon international airport west of Seoul.
They had been planning to attend a seminar on nuclear power in the South Korean capital.
An immigration official confirmed the action and said both would be deported later on Monday.
"Their entry was denied at the request of security authorities because their activities here may hurt our national interests," the official, who declined to be identified, told AFP.
According to Greenpeace, six of its staff from Greenpeace International and Greenpeace East Asia have been denied access to South Korea since last November.
"Korea is investing in dangerous nuclear technology when it could be replacing nuclear with renewable energy," Beranek said in a statement released by Greenpeace after he had been stopped at immigration.
"Instead of allowing a full discussion of the terrible risks of nuclear power, the government chooses to silence critics and try to hide the concerns," Beranek said.
South Korea operates 23 nuclear power reactors which meet more than 35 percent of the country's electricity needs. It plans to build an additional 16 reactors by 2030.
The government has vowed to stick to its nuclear power programme despite public concerns arising from last year's nuclear disaster in Japan.
Last week, South Korea shut down two 1,000-megawatt nuclear reactors at separate plants, following apparently unrelated systems malfunctions that triggered calls for a safety review.
