SEOUL, South Korea (CNN) -

North Korea says it plans to prosecute two American tourists that it detained earlier this year, accusing them of "perpetrating hostile acts."

The North Korean government had previously said it was holding the two U.S. citizens, Jeffrey Fowle and Matthew Miller, but hadn't said what it planned to do with them.

"According to the results of the investigation, suspicions about their hostile acts have been confirmed by evidence and their testimonies," the North's Korean Central News Agency (KCNA) reported Monday.

"The relevant organ of the DPRK is carrying on the investigation into them and making preparations for bringing them before court on the basis of the already confirmed charges," the report said, using using an abbreviation of the country's official name, the Democratic People's Republic of Korea.

The U.S. State Department called on North Korea to release the two men on humanitarian grounds.

Asylum bid?

North Korea said in late April that it had taken Miller into custody, claiming he had come to the country seeking asylum and had torn up his tourist visa.

It announced the detention of Fowle in early June, saying he had violated the law by acting "contrary to the purpose of tourism."

It didn't provide details at the time on what exactly he was accused of doing. But the Japanese news agency Kyodo cited unidentified diplomatic sources as saying that Fowle was part of a tour group and that he was detained in mid-May after allegedly leaving a Bible in a hotel where he had been staying.

Although North Korea regularly denounces the United States as a sworn enemy in its state-run media, Americans are able to visit the country as tourists. But the U.S. State Department says it "strongly recommends against all travel by U.S. citizens to North Korea."

Swedish Embassy involved

"Contact with an official looking after consular affairs, treatment, etc. in the course of investigation are being made in line with the laws of the relevant country," KCNA said Monday.

In practice, that means that North Korean authorities have been in touch with the Swedish Embassy, which represents American interests in the country.

"Out of humanitarian concern for Mr. Fowle and Mr. Miller and their families, we request North Korea release them so they may return home," said U.S. State Department spokeswoman Jen Psaki.

She said the Swedish Embassy had carried out visits to both men in North Korean custody.

Kenneth Bae case

North Korea is also holding Kenneth Bae, a Korean-American missionary who was sentenced to 15 years hard labor in 2013 by a court that said he had carried out acts aimed at bringing down the regime of leader Kim Jong Un.

Psaki on Monday repeated a request for Bae to be pardoned and released.

Although North Korea contains a number of state-controlled churches, the totalitarian regime forbids independent religious activities, viewing them as potential threats to its authority.

Other Americans detained in the North have later been released.

Last year, Pyongyang freed Merrill Newman, an 85-year-old veteran of the Korean War who was on an organized private tour in the country, after holding him for several weeks.