A China-based travel agency says an American university student recently detained by North Korea is being held over an unspecified incident at his hotel before he was scheduled to board a flight for Beijing.

Gareth Johnson of Young Pioneer Tours said via email Saturday that Otto Warmbier had been staying at Pyongyang's Yanggakdo International Hotel and was not with other tourists when the incident occurred. The company in a statement said Warmbier was detained at the Pyongyang Airport on Jan. 2.

Warmbier is from Ohio and was studying finance at the University of Virginia.

North Korea has accused Warmbier of committing a "hostile act" orchestrated by the U.S.

The U.S. and South Korea have been pushing for tough sanctions against the North over its latest nuclear test on Jan. 6.