At a Ministry of Foreign Affairs briefing Tuesday, a spokesman said that Gui Minhai, who was apprehended by plainclothes police on a train in January
in front of Swedish diplomats, had been "subjected to criminal coercive measures."
"Gui Minhai broke Chinese law and has already been subjected to criminal coercive measures in accordance with the law by relevant Chinese authorities," Foreign Ministry spokesman Geng Shuang said, also criticizing a Swedish statement issued Monday.
"I want to once again stress that China opposes any form of speech or actions that ignore China's legal sovereignty."
On Monday the Swedish Ministry of Foreign Affairs called the arrest and detention of its citizen a "very serious matter," and said it contravened "basic international rules on consular support."
"The brutal intervention in January against a Swedish support operation was conducted in spite of repeated assurances from the Chinese authorities that Mr Gui was free at that time," said the statement, attributed to Swedish Foreign Minister Margot Wallstrom.
"The current situation also raises questions about the application of the rule of law, including the prohibition of arbitrary deprivation of liberty. 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."
The Foreign Affairs spokesman, Geng, said that, "Although Gui Minhai is a Swedish citizen, the case he is involved in must be handled in accordance with Chinese law. China and Sweden are maintaining open communication channels on this case."
Gui, 53, who wrote and published numerous titles critical of the Communist leadership, was traveling to Beijing to be examined by a Swedish doctor at the embassy when he was taken, his daughter Angela told Radio Sweden last month.
"He was escorted on this train journey on Saturday by two diplomats and they were on the train for about five hours," she said.
"At one of the stops before Beijing, there were about 10 men in plainclothes that came in and said they were from the police, and just grabbed him and took him away. After that, I have not heard anything."
Gui had been diagnosed with the progressive neurodegenerative disease known as ALS, his daughter said.
On Tuesday, Geng slammed Sweden's handling of the incident and said that the European country should not do anything that would adversely affect bilateral relations.
"China absolutely does not accept Sweden's ignoring China's notifications and repeatedly making irresponsible remarks. We strongly call on Sweden not to do things that may damage mutual trust and the macro bilateral relations between the two countries."
It's the second time in just over two years that Gui has been allegedly seized by Chinese agents. He first vanished in late 2015 from his holiday home in Thailand.
Gui was one of five Hong Kong-based booksellers who disappeared in mysterious circumstances in late 2015 before resurfacing in Chinese police custody. They were all involved in publishing political gossip about China's Communist leaders, including President Xi Jinping.
Amid intense speculation about his possible kidnapping by Chinese government agents, a tearful Gui was paraded on state broadcaster CCTV in January 2016. During the appearance, he said he had returned to China from Thailand voluntarily to clear his conscience over a fatal drunk-driving accident more than a decade earlier.