A student activist who helped run last year's Hong Kong protests has been denied entry to Malaysia by immigration authorities.
Joshua Wong, 18, had been invited to the country to take part in academic talks on democracy in China.
He was detained shortly after arriving at an airport on the northern island of Penang and sent back to Hong Kong.
The organisers of the event at which Mr Wong was due to speak have demanded to know why he was refused entry.
"We're angry at the government's actions," said Ng Yap-hwa, a human rights activist.
"There's no reason that the Malaysian government should stop us from organising any international talk on the democracy movement."
Penang immigration authorities have yet to comment.
Mr Wong was one of the main leaders of the Hong Kong protests, which saw tens of thousands of demonstrators flood the streets demanding the right to fully free leadership elections.
He was arrested twice and took part in a hunger strike in a bid to force the Beijing and Hong Kong governments to engage in talks about the 2017 election.
His Facebook page showed he had been invited to participate in a series of seminars across Malaysia including one in the capital, Kuala Lumpur.
Writing on the social networking site he said: "Malaysia's government doesn't allow me to enter, now on my way back to Hong Kong."
Mr Wong said a Malaysian immigration official told him a "government order" had been given to deny him entry.
Home Minister Ahmad Zahid Hamidi said he had knowledge of the incident, according to news website Malaysiakini.
A spokesman for Hong Kong's immigration department said the entry of its residents to other countries was "out of the control of the Hong Kong government".