An investigation has been launched into a threatening letter found at the U.S. Embassy in Seoul, police said Thursday.
The Seoul Metropolitan Police Agency (SMPA) said the letter was delivered to the embassy in downtown Seoul on Monday that contained threats against American citizens in South Korea.
The letter, which was also written in Korean, said in English, "American citizens living on the territory of South Korea will be subject to the attack if they continue with a war game," according to the SMPA.
The letter also attached a photo of a pressure-cooker bomb similar to the ones used in the Boston Marathon terrorist attack last month, police officers said.
While it is not immediately known who was behind the incident, police officers said they are open to the possibility that it could be the same suspect who threatened the South Korean defense minister last week.
Defense Minister Kim Kwan-jin received a similar parcel containing a threatening letter and suspicious white powder on April 23, which turned out to be wheat flour.
Police said they have raided the house of a prime suspect behind the parcel incident but failed to find or seize any relevant proof.