Authorities at Incheon International Airport say they received on Sunday a letter threatening to bomb U.S.-bound airplanes.

According to airport authorities and police, the one page letter, posted from Thailand, stated that an Indian terrorist would destroy planes scheduled to leave the airport for the United States beginning this and next month.

Earlier this month, the U.S. Embassy in Seoul received a similar threatening letter that was also reportedly sent from Thailand.

As a result, police are trying to identify the delivery process of the letters and have heightened security searches of the luggage of Indian passengers that enter and leave the airport.