SEOUL, South Korea — A Korean-American sentenced to 15 years hard labor in North Korea was a missionary who used his tourism business to form groups to overthrow the government, the state's Supreme Court said.

Kenneth Bae, 44, was sentenced earlier this month after being detained late last year leading a tour group in the North Korean city of Rason, on the border with China.

"In order to carry out the plan he infiltrated at least 250 students who had been educated at the plot-breeding bases operated by him into Rason City disguised as tourists," a court spokesman told North Korea's KCNA news agency in a report issued early on Friday.

Bae has acknowledged being a missionary and said he conducted services in the North, according to an audio sermon and note posted on the website of a Korean Presbyterian church in St. Louis in the United States.

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Recordings on the church's website showed him talking of a trip to Rason in 2011 where he left his North Korean minders behind and hiked to the top of a mountain where he and the group of people accompanying him prayed.

Bae said he had been moved by his faith to preach in North Korea, ranked the most hostile to Christianity by Open Doors International, a Christian advocacy and aid group, since the late 2000s.

"I know Jesus wants me to become a path to North Korea," Bae said in the remarks at the St. Louis church in December 2011, of which an audio recording was posted on the church's website.

Church officials declined to comment on the contents of the website. The recording has since been removed.

Washington has appealed for Bae's release. In previous cases of Americans being imprisoned in North Korea, their release has been secured by high profile visits as the two countries do not have diplomatic relations.

Bae's case was handled by the Swedish embassy in Pyongyang, which has declined to comment on the case.

Two U.S. journalists sentenced to 12 years in 2009 were released only after a visit by former President Bill Clinton.

Bae, a South Korean-born naturalized American was first sent to China for a two-month mission trip by Hawaii-based evangelical group Youth With a Mission (YWAM) in 2006, according to his posts and the KCNA report.

A Christian source in the United States who is familiar with Bae's missionary activities in China said he ran an English language school in the port city of Dalian. He declined to be identified due to the sensitivity of the case.

Bae moved to the Chinese border city of Dandong in 2010 and carried out his own mission work inside North Korea, according to the St Louis church web-page.

"From this year, I am working at taking short-term mission teams into North Korea," Bae said in the audio recording. "North Korea is a special place where a small number of people are working . . . it would be good if people worshipping and praying could live in this land."

North Korea has religions denominations including Protestant and Catholic churches but services and activities are strictly under state control and there is no freedom of worship, Christian groups say.

The two Protestant churches in Pyongyang are viewed as showcases where North Korea takes visitors to advertise its claim to religious freedom.

OFFICIAL INVITATION

Unlike other Americans, largely of Korean descent, who have been arrested for entering North Korea illegally, Bae was a legitimate visitor with an official invitation at least in 2011, according to his audio recording on the church website.

The Christian source described Bae as a devoted Christian missionary with good intentions.

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"He is a good-natured person and not like someone who plots a big thing. He was a kind of helping man, not a person trying to overthrow a government," the source said.

North Korean state media said Bae's crimes could have been punished by death but the sentence was cut to 15 years hard labor after he admitted the charges.

On one of his trips, Bae recalled singing hymns together with his mission tourists at a beach surrounded by North Koreans.

One tourist said Amen in English at the end of the singing.

"That was bad. They [North Koreans] all understood Amen," Bae said.