Wei Jingsheng, a U.S.-based Chinese democracy activist who was planning to attend an event in Tokyo marking the 18th anniversary of the Tiananmen Square demonstrations on Sunday, was denied entry at Narita International Airport.
Flying in from New York on Saturday, he did not have an entry visa.
Organizers of the event said Wei, 57, was refused entry despite previous assurances from Japanese immigration authorities that he could stay in Japan as long as he was on a transit stay even though his travel document was expiring.
Immigration authorities declined to comment on Wei's individual case but said that in principle a Chinese national needs a visa even on a transit if the person wishes to attend an assembly.
Wei arrived at Narita at noon Saturday using a re-entry certificate of the U.S. government, one of the event organizers said. He was going to give a speech at a meeting to be held Sunday evening in Tokyo to commemorate the 18th anniversary of the 1989 Tiananmen crackdown on prodemocracy activists.
He was then to fly to Guam and revisit Japan.
Wei spent Sunday at an airport hotel in Narita and was due to be flown back to New York.
He visited Japan last year to give speeches at the invitation of a citizens' group.
Wei was twice imprisoned in China for political reasons. He was temporarily released in 1997 after spending a total of 18 years behind bars. He then moved to the U.S.