China confirmed on Tuesday that it had detained Gui, a Hong Kong-based bookseller, after his daughter said Chinese police had seized him from a train last month.
In 2015, Gui was abducted in Thailand while on holiday, one of five Hong Kong booksellers who went missing that year and later appeared in mainland Chinese custody. The four others have returned to Hong Kong.
Swedish Foreign Minister Margot Wallstrom said in a statement on Monday that Gui's detention was a "very serious matter" and that China's "brutal" intervention in Sweden's attempts to assist Gui, who Chinese authorities had said had been freed, represented a contravention of international rules on consular support.
"European countries and the US should educate their newly naturalised citizens that the new passport cannot be their amulet in China. If they conduct activities in China, they must obey Chinese law," an editorial in the Global Times said.
It said Gui, who was born in China and later became a Swedish citizen, often returned to China.
"There are many other 'foreigners' like Gui working and living in China. A few of them take advantage of their double identity as both Chinese and foreigner to seek profits and wish to shield themselves from penalties if they breach the law," the newspaper said.
"Sweden's expectation to strengthen consular assistance to Gui cannot transcend China's legal procedures," it said.
Calls for Gui's release reflected an "extraterritorial mentality", it added.
"Gui committed a crime in China and China is handling his case according to its law," it said.
"Now Western public opinion defined the case as political persecution of people with foreign citizenship, arbitrarily demanding China act according to their will. With such contempt toward Chinese law, is there any room for communication?"
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