Prominent Hong Kong pro-democracy activist Joshua Wong on Tuesday was denied entry into junta-run Thailand, where he planned to give a speech commemorating the massacre of students.

Nineteen-year-old Wong, who helped organize 2014's "Umbrella movement" protests against Beijing's interference in Hong Kong elections, was then deported on Wednesday after spending several hours detained at Bangkok's Suvarnabhumi airport.

Demosisto, the party Wong helped co-found, said in a statement that it "strongly condemns the Thai government for unreasonably limiting Wong's freedom and right to entry."

Wong's supporters blamed China for putting pressure on Thailand and expressed concern the junta government would hand the activist over to Beijing. A Hong Kong bookseller was handed over to China last year.

'Various factors'

In a statement, the Thai Foreign Ministry said the denial of entry "involves various factors."

Wong was scheduled to give a speech on Thursday at an event in Bangkok commemorating the Thammasat massacre, when pro-democracy students were killed by Thai security forces in 1976.

Wong wrote on Facebook prior to his departure to Bangkok that he was concerned about the trip.

"We all know Thailand is not politically stable... It is also clear that it is close to the Chinese Communist Party," he said.

Last year, Wong was denied entry into Malaysia, where he had planned to give talks on democracy in China.

The US Embassy in Bangkok said it was monitoring events and supported freedom of expression.

"We support individuals exercising their universally recognized fundamental freedoms of opinion expression peaceful assembly and association throughout the world," said Embassy spokesman Steve Castonguay.

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cw/es/bw,kl (AFP, AP, Reuters)