SEOUL, Dec. 26 (Xinhua) -- Three South Korean workers in a nuclear reactor's construction site were suffocated for unidentified reasons, Yonhap News Agency reported Friday.

The workers were suffocated at about 5:18 p.m. local time at the construction site for the Shin Gori No. 3 reactor in the country's southeast city of Ulsan.

The reactor operator was quoted as saying that hydrogen gas was believed to be leaked at the site, but the exact cause is still under investigation.

The workers suffering from gas suffocation were taken to nearby hospitals.