BEIJING — Sweden has condemned China’s “brutal” detention of Swedish citizen Gui Minhai, escalating a standoff sparked two weeks ago when Chinese agents seized the Hong Kong-based bookseller as he was traveling with Swedish diplomats.

In a sharply worded statement on Monday, Foreign Minister Margot Wallstrom questioned the rule of law in China and characterized Gui’s detention on Jan. 20 on a Chinese train as “contrary to basic international rules on consular support.” She demanded that China disclose Gui’s whereabouts and his alleged crime.

“The brutal intervention in January against a Swedish support measure was implemented despite Chinese repeated assurances that Gui Minhai was a free man at the time,” Wallstrom said.

Hours later, on Tuesday, Chinese foreign ministry spokesman Geng Shuang hit back at Sweden for “irresponsible” comments and told reporters at a regular briefing that Gui was being held lawfully under “coercive measures,” without giving details. The term is a euphemism for detention.

Wallstrom’s statement marks a tougher stance from Sweden two weeks after 10 Chinese security agents seized Gui as he traveled to Beijing accompanied by two consular officials to seek medical treatment. Stockholm’s initial silence over the incident drew criticism from activists and the media in Sweden and beyond.

Gui, 53, sold gossipy books about Chinese leaders in the semi-autonomous city of Hong Kong before he disappeared for the first time in 2015, when he was believed to have been abducted by Chinese agents from his seaside home in Thailand. At the time, speculation swirled in publishing circles that Gui was on the verge of releasing a new book about a former mistress of the Chinese president, explaining the all-out efforts to silence him.

He was released into house arrest in October in the eastern city of Ningbo after Chinese authorities said he turned himself in over a hit-and-run accident allegedly committed years before.

Western officials say they had assurances early this year from China’s foreign ministry that Gui’s liberty had been restored, but agents believed to be from China’s state security apparatus, possibly fearing that Gui would leave the country, seized him a second time in January.

Geng, the ministry spokesman, did not respond Tuesday to Sweden’s demand that Gui’s alleged crimes be disclosed and instead chastised Stockholm for going public with its criticism.

“The Swedish side should know well about the seriousness of the case, as well as the disgraceful roles that certain Swedish people played in the case,” Geng said. “China will by no means accept the irresponsible remarks made by the Swedish side repeatedly in defiance of our notice.”

Germany’s ambassador to China, Michael Clauss, on Tuesday backed Sweden’s statement, saying “there is no doubt that Sweden has the support of all of us as members of the EU.”

U.S. State Department spokeswoman Heather Nauert and European Union ambassador Hans Dietmar Schweisgut have also called on China to immediately release Gui.

Gui was one of five Hong Kong booksellers whose disappearances symbolized China’s determination to enforce its hard line on squelching political dissent and a free press despite international criticism.

William Nee, China researcher for Amnesty International, called Gui’s detention a “brazen and outrageous move by the Chinese authorities.”

“It is ludicrous for the Chinese government to lecture others about respect, when they have shown utter contempt for fair trials and other human rights,” Nee said in an emailed statement on Tuesday. — AP