BEIJING/STOCKHOLM (REUTERS, AFP) - China confirmed on Tuesday (Feb 6) that it had detained Swedish citizen and Hong Kong-based bookseller Gui Minhai, after his daughter said Chinese police had seized him from a train last month.

One of five Hong Kong-based booksellers known for publishing gossipy titles about Chinese political leaders, Gui first vanished in 2015 while on holiday in Thailand.

He eventually surfaced at an undisclosed location in China, confessing to involvement in a fatal traffic accident and smuggling illegal books.

China's foreign ministry had previously said that Gui, 53, was released in October last year after serving a sentence for a traffic offence in 2003. But his daughter Angela Gui, 23, told AFP that he was under "loose house arrest" in the eastern mainland city of Ningbo, where some of his relatives still live. The four other booksellers have returned to Hong Kong.

Gui's daughter said in January that her father was taken from a Beijing-bound train while in the company of two Swedish diplomats who were escorting him to seek medical attention for a neurological disorder.

Swedish Foreign Minister Margot Wallström said in a statement on Monday that Gui's continued detention is a "very serious matter" and that China's "brutal" intervention in Sweden's attempts to assist Gui, who Chinese authorities had said was free, represents a contravention of international rules on consular support.

"We demand that our citizen be given the opportunity to meet Swedish diplomatic and medical staff, and that he be released so that he can be reunited with his daughter and family."

Asked about the statement, Chinese foreign ministry spokesman Geng Shuang said that China cannot accept such "irresponsible" statements from Sweden.

"Gui Minhai broke Chinese law and has already been subjected to criminal coercive measures in accordance with the law by relevant Chinese authorities," Geng told a regular briefing. The term "coercive measures" generally refers to detention in China.

"Although Gui Minhai is a Swedish citizen, the case he is suspected of must be handled in accordance with Chinese law," he said. Sweden should understand the serious nature of the case and the "disgraceful" role played by certain Swedish people, Geng said, without giving details.

Civil society has come under increasing pressure since Chinese President Xi Jinping took office in 2012, with authorities rounding up hundreds of lawyers and activists.

The United States and European Union have called for Gui Minhai's immediate release and his disappearance has sparked a diplomatic row between Stockholm and Beijing.

Angela Gui fears he may now be put on trial and receive a longer sentence, jeopardising his health.

Doctors in Ningbo said her father may have the neurological disease ALS - he had been on his way to Beijing to see a Swedish specialist.

"If he does have ALS, perhaps he might not have that much time left," she told AFP.

China was widely criticised after veteran rights activist and Nobel Peace Prize Laureate Liu Xiaobo died from liver cancer while on medical parole in July last year.

Rights groups had pushed for him to be allowed to seek medical treatment abroad. It was the first time a Nobel laureate had died in custody since Nazi Germany.

Angela Gui said the international community must snap out of its "paralysis" over the case, describing her frustration that more had not been done to get her father out of China sooner.

"He shouldn't have been abducted again in the first place - there should have been a way of getting him home before that," she said.

"Or there should have been a way of making sure he was safe when he was travelling."