Pyongyang's Korean Central News Agency said in a short dispatch Friday that the North decided to indict the women reporters "based on criminal data confirmed."
Laura Ling and Euna Lee, journalists working for former Vice President Al Gore's San Francisco-based Current TV, were arrested after they allegedly crossed the border from on March 17 while reporting on North Korean refugees.
The North said last month it would indict them on charges of unspecified "hostile acts."
If convicted of espionage, the women could face at least five years in prison under North Korean law.
Investigators were poring through the journalists' notebooks, videotapes and camera for signs they were spying on the North's military facilities, the JoongAng Ilbo newspaper said last month, citing an unnamed South Korean intelligence official.
The two were being held at private quarters run by North Korean military intelligence agency on the outskirts of the capital, the report said.
's main spy agency, the National Intelligence Service, said South Korean and U.S. intelligence authorities were keeping a close watch on the case but that it could not immediately confirm the report.
The U.S. State Departement has also been in contact with the communist state about the journalists' detention.
An activist who claims he helped the two plan their reporting trip has said they were reporting on North Korean refugees in China. The Rev. Chun Ki-won told The Associated Press that he warned them against getting too close to the border with North Korea.
JoongAng said they crossed into far northeastern North Korea by walking over the Tumen River dividing the country from China early in the morning of March 17. The narrow river, frozen this time of year, is a frequent escape route for refugees fleeing North Korea.
The two journalists were stopped by a North Korean soldier and then taken into custody when their IDs revealed they were American citizens, the report said, citing unnamed sources. The two reportedly were taken to Pyongyang on Wednesday in separate vehicles.
If convicted on espionage charges, the women face at least five years in prison under North Korean law, South Korea's Unification Ministry said.
However, JoongAng Ilbo noted that conviction on charges of illegally crossing the border and spying on the North's military facilities could draw more than 20 years for each.
Past detentions of Americans have required international intervention. In 1996, New Mexico Gov. Bill Richardson, then a congressman, went to North Korea to help secure the release of an American detained for three months on spying charges. In 1994, he helped arrange the freedom of a U.S. soldier whose helicopter had strayed into North Korea.