(CNN) -- The Korean-American who has been held in North Korea since November entered the country on a valid tourist visa, a senior U.S. official told CNN on Monday.
The U.S. State Department on Monday publicly called on the North to release Kenneth Bae on humanitarian grounds.
Spokesman Patrick Ventrell told reporters that Swedish diplomats, who represent U.S. interests in North Korea because Washington has no diplomatic relations with the North, were able to visit Bae, a U.S. citizen, on Friday.
Some Americans have previously crossed the border without a visa, either knowingly or by mistake, but in this case, the official said, "This was somebody who was a tour operator who has been there in the past and has a visa to go to the North."
The official, who spoke on background because of the diplomatic sensitivity of the issue, says the State Department doesn't know the exact charges against Bae -- whom the North refers to by his Korean name, Pae Jun Ho -- and is trying to clarify the matter through the Swedish Embassy.
Media reports have listed the charges as plotting to overthrow the government, which carry penalties including death or life imprisonment.
"In the past there have been many clear instances where American citizens are used as political bargaining chips, and our concern is that this individual not be used in this matter," the official added.
North Korea plans to hold a trial against Bae, state media said Saturday, complicating tense relations between the North and the United States.
Bae entered North Korea as a tourist on November 3, according to the Korean Central News Agency.
According to the news agency, Bae confessed to an offense, but the KCNA did not say what it was.
"He will soon be taken to the Supreme Court of the DPRK to face judgment," the news agency said, using the official name of the country, the Democratic People's Republic of Korea.
The developments come amid tense relations between North Korea and South Korea and the United States. In recent weeks, the North has intensified threats against its neighbor and the United States.
CNN's Elise Labott and Karen Smith contributed to this report.