Below is an article published by Wall Street Journal :

South Korean immigration authorities stopped a prominent Uighur activist, Dolkun Isa of Germany, from entering the country for a conference on democracy, the government confirmed Thursday (17th September).

Mr. Isa, secretary-general for the World Uighur Congress, flew to Seoul's international airport on Tuesday but wasn't allowed to enter the country. A spokesman for South Korea's Justice Ministry said Thursday that he couldn't discuss why Mr. Isa wasn't permitted entry.

Mr. Isa remained at the airport Thursday morning and it wasn't clear when he would depart. The conference he was scheduled to attend, called the World Forum for Democratization in Asia, began Wednesday and continues through Friday.

Mr. Isa fled China in 1997 and was given asylum in Germany that year. He became a German citizen in 2006. Chinese authorities for years have alleged Mr. Isa is a terrorist.
Earlier this year, Taiwanese news media falsely reported that Mr. Isa had secretly entered the country, leading Taiwanese immigration authorities to declare that he would be barred from there. Mr. Isa was at home in Germany as that episode unfolded.
In the past two days, several non-governmental organizations sent letters to South Korean government agencies in protest of the decision not to allow Mr. Isa into the country.