Chinese security officers detained a group of Hong Kong university students for two days at the Mount Everest base camp in Tibet because one of them was holding a sign reading “Liberate Hong Kong.”

“After investigation, it was confirmed that the man’s behavior had violated regulations on the law of the People’s Republic of China on Penalties for Administration of Public Security. The public security institution warned him according to law,” said a statement from the Cyber Security Force of the Tibet Autonomous Region Security Bureau posted Monday on China’s Weibo social media service.

The statement said the student admitted “wrongdoing,” promised not to break Chinese law again, and signed a “statement of repentance.” He was released on Monday along with his traveling companions, fellow students from two Hong Kong universities who do not appear to have been charged with any offense but were detained anyway.

A Hong Kong protest flag was planted by other activists atop Mont Blanc in the Alps over the weekend.

#HongKongProtest slogan “Reclaim Hong Kong, Revolution of Our Times” brought to the top of Mont Blanc in the Alps. Photos from Facebook Page: 山中遊子 pic.twitter.com/xZI40JY1vU — Rachel Cheung (@rachel_cheung1) August 23, 2019

The flag on Mont Blanc has a black background with white Chinese letters reading, “Reclaim Hong Kong, Revolution of Our Times.”