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An American detained for nearly six months in North Korea has been sentenced to 15 years of labor for crimes against the state, the North's state media said Thursday, a development that further complicates already strained ties between Pyongyang and Washington.

The sentencing of Kenneth Bae, described by friends as a devout Christian and a tour operator, comes amid signs of tentative diplomacy following weeks of rising tensions in the region. North Korea had been warning of nuclear war and missile strikes, an angry response to U.N. sanctions for conducting a long-range rocket launch in December and a nuclear test in February, as well as U.S.-South Korean military drills in South Korea.

Analysts say Pyongyang could use Bae as a bargaining chip as it seeks dialogue with Washington.

In Washington, the U.S. State Department had no immediate comment.

It's not the first time an American has been arrested and sentenced to labor during a nuclear standoff.

In 2009, after Pyongyang's launch of an earlier long-range rocket and its second underground nuclear test, two American journalists were sentenced to 12 years of hard labor after sneaking across the border from China.

They later were pardoned on humanitarian grounds and released to former U.S. President Bill Clinton, who flew to Pyongyang on a rescue mission. He also met with then-leader Kim Jong Il, which paved the way for talks.

Bae's trial on charges of "committing hostile acts" against North Korea place in Supreme Court on Tuesday, the state-run Korean Central News Agency reported.

He was arrested in early November in Rason, a special economic zone in North Korea's far northeastern region bordering China and Russia, state media said. The exact nature of Bae's alleged crimes has not been revealed.

Friends and colleagues say Bae, a Korean American who was living in Washington state, was based in the Chinese border city of Dalian and traveled frequently to North Korea to feed orphans.

State media refers to Bae as Pae Jun Ho, the North Korean spelling of his Korean name.

Bae is at least the sixth American detained in North Korea since 2009. The others eventually were deported or released.

Three other Americans detained in recent years were also devout Christians. While North Korea's constitution guarantees freedom of religion, in practice only sanctioned services are tolerated by the government.

North Korea may be fishing for another visit by a high-profile American envoy, said Ahn Chan-il, head of the World Institute for North Korea Studies think tank in South Korea.

"North Korea is using Bae as bait to make such a visit happen. An American bigwig visiting Pyongyang would also burnish Kim Jong Un's leadership profile," Ahn said.