A U.S. citizen has been put under a 10-day detention in China for carrying and concealing hazardous materials while trying to board a flight from Beijing to Munich last week, Chinas aviation authority said Monday.

A spokesman for the Civil Aviation Administration of China (CAAC) said the American suspect was intercepted at the Beijing Capital International Airport at about 1:00 a.m. on Sept. 5, when he was trying to board Air China flight CA961 from Beijing to Munich.

Police found that the man was carrying a bottle of liquid containing trans-Methyl crotonate, which is prohibited aboard a flight in China.

As the man violated the law on public security administration punishments, he was subject to a penalty of 10-day administrative detention, the spokesman said.

CAAC declined to disclose the name of the passenger.