Story highlights Kenneth Bae, referred to as Pae Jun Ho by North Korea, is sentenced, KCNA reports

He was accused of serious crimes; a U.S. official wasn't sure what the claims were

The U.S. had pushed for Bae's release on humanitarian grounds

An American man detained in North Korea since last November has been sentenced to 15 years of hard labor, North Korean state news reported Thursday.

A story on the KCNA website indicated that Pae Jun Ho had been sentenced by North Korea's supreme court. The North has used that name to refer to the man U.S. authorities call Kenneth Bae.

A Korean-American, Bae entered North Korea on a valid tourist visa, a senior U.S. official told CNN on Monday. The official -- who spoke on background because of the diplomatic sensitivity of the issue -- said then that the State Department didn't know the exact charges against Bae.

The KCNA report indicated that the American was sentenced Tuesday for "carrying out serious crimes" against North Korea, without specifying what exactly he allegedly had done. He was arrested November 3 in Rason City.

The U.S. State Department had appealed Monday for Bae's release on humanitarian grounds. Three days earlier, a State Department spokesman 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.

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Some Americans have previously crossed the border without a visa, either knowingly or by mistake, but in this case, the U.S. 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."

Bae's sentencing comes amid tense relations between North Korea and both the United States and its staunch ally South Korea. In recent weeks, the North has intensified threats against its neighbor and the United States.