An employee of the United Kingdom’s consulate in Hong Kong was arrested in mainland China, the two governments confirmed, amid tensions over protests in the former British colony.

“Shenzhen police ordered him to serve 15 days of administrative detention for violating public security management regulations,” Chinese foreign ministry spokesman Geng Shuang said Wednesday.

That statement broke China’s silence about the disappearance of trade and investment officer Simon Cheng, 28, whose family reported him missing Aug. 9. The arrest raises suspicions that China is retaliating for Britain's rhetorical support for the pro-democracy protests that have gripped Hong Kong this summer.

“Simon traveled to mainland China to attend a work-related conference and we are extremely concerned that he has not returned to Hong Kong,” a spokesman at the United Kingdom’s Foreign and Commonwealth Office told the Washington Examiner. “That’s why we have repeatedly raised the case with the Hong Kong and Chinese authorities about why Simon was detained. We remain in close contact with his family.”

Cheng was detained attempting to return from a day trip to the mainland on Aug. 8. “At first I didn’t want his case to go public because I was worried exposure would further jeopardize him,” his girlfriend, who asked to be identified by her surname, Li, said Wednesday. “But now I really don’t know what else I can do.”

The publicity led to the confirmation of his detention, but China dismissed the ensuing British rebuke.

“This worker is a Hong Kong citizen — not a British citizen — and he is Chinese,” Geng said. “And this is entirely an internal matter of China.”

Geng reiterated China’s accusation that Western countries, including the United States and the United Kingdom, have stoked the mass protests against Beijing’s encroachments on Hong Kong’s semi-autonomous status.

“As for Britain’s comments, we’ve made stern representations to Britain for the series of comments and actions they’ve made on Hong Kong,” he said.

The protests began when Hong Kong's Beijing-backed local government tried to pass an extradition bill that would allow its residents to be taken into custody by mainland authorities based on flimsy evidence. Dissidents have denounced the proposal as “legalized kidnapping” that would be abused for political purposes.

Cheng had similar worries about his own trip. “Ready to pass through the border … pray for me,” he wrote in an Aug. 8 text message to his girlfriend. She said the two had discussed marriage but he didn't want to move back to her homeland of Taiwan, where they met. “He said he loves Hong Kong and wanted to sacrifice all he has for his motherland," she said.