North Korea said it will soon put a detained American on trial for allegedly trying to overthrow the government.
The announcement further complicates the already fraught relations between Pyongyang and Washington.
The indictment of Kenneth Bae comes in the middle of something of a lull after weeks of threats by North Korea against the US and South Korea.
North Korea has expressed rage over UN sanctions over a February nuclear test and ongoing US-South Korean military drills, though analysts say Pyongyang's motive is to get its Korean War enemies to negotiate on its own terms.
Bae, identified in North Korean state media by his Korean name, Pae Jun Ho, is a tour operator of Korean descent who was arrested after arriving with a tour on November 3 in Rason, a special economic zone bordering China and Russia.
He is the sixth American detained in North Korea since 2009. The other Americans were eventually deported or released after high-profile diplomatic interventions, some involving former Presidents Bill Clinton and Jimmy Carter.
Analysts say the North will probably hand Bae a harsh punishment to use him as a bargaining chip in possible negotiations with the US.
"The preliminary inquiry into crimes committed by American citizen Pae Jun Ho closed," the official Korean Central News Agency said in a brief report. "In the process of investigation he admitted that he committed crimes aimed to topple the DPRK ( the Democratic People's Republic of Korea) with hostility toward it. His crimes were proved by evidence."
Under North Korea's criminal code, terrorist acts include murdering, kidnapping and injuring the country's citizens can lead to a death sentence or life in jail.
North Korea and the US fought the 1950-53 Korean War and still do not have diplomatic relations.