It is thought that the women were researching North Korean refugees
Two US reporters held in North Korea earlier this month will be tried for illegal entry and "hostile acts", the country's state-run news agency says.
The Korean Central News Agency (KCNA) said preparations were under way for indictments and a trial.
Euna Lee and Laura Ling were detained on 17 March on North Korea's border with China.
The move comes amid growing tension in the region ahead of North Korea's controversial satellite launch.
The North says the launch is part of its communications programme, but the US fears this is a cover for testing long-range missile technology.
The United States says it is pursuing all diplomatic means available to secure the release of the two American women.
"The illegal entry of US reporters into the DPRK (Democratic People's Republic of Korea) and their suspected hostile acts have been confirmed by evidence and their statements," the KCNA said.
It said "a competent organ... is carrying on its investigation and, at the same time, making a preparation for indicting them at a trial on the basis of the already confirmed suspicions".
Euna Lee, a Korean-American, and Laura Ling, a Chinese-American, work for Current TV in California.
There is still some confusion as to exactly where the reporters were arrested.
South Korean television station YTN and unnamed diplomatic sources said that North Korean guards crossed the Tumen river into Chinese territory to arrest the journalists.
Pyongyang says the reporters crossed its border illegally.
"The United States continues to work on this matter through diplomatic channels," an unnamed senior White House official told the AFP news agency.
"We have seen the brief North Korean press report (on the trial)," the official is quoted as saying. "We have no higher priority than the protection of American citizens abroad."
The US state department said a Swedish envoy acting on behalf of Washington, which has no diplomatic relations with Pyongyang, had visited the journalists for the first time over the weekend.
"A representative of the Swedish embassy met with each one individually," spokesman Gordon Duguid said. He gave no further details of the women's condition or where they were being held.
North Korea has in the past freed Americans it has detained but only after diplomatic intervention.
The Committee to Protect Journalists issued a statement expressing concern about the North's action against the reporters.