The United States is calling on North Korea to release a Korean-American Christian sentenced to 15 years of hard labor, CBN News reports. Washington state resident Kenneth Bae, 44, entered North Korea on a tourist visa and was arrested Nov. 3 in the city of Rason, near the border with China and Russia. North Korea's Supreme Court convicted Bae of attempting to topple the government and other unspecified "hostile acts" against the state. "We've had long-standing concerns about the lack of transparency and due process in the North Korean legal system," U.S. State Department spokesman Patrick Ventrell said. "So, now that Mr. Bae has gone through the legal process, we urge the DPRK to grant him amnesty and immediate release." Friends and colleagues say Bae is a devout Christian who frequently traveled to North Korea to feed orphans; Doo Hee Yoon, an activist based in South Korea, told AFP he may have been detained for photographing emaciated children. Bae is the sixth American to be detained by the Communist state since 2009, and his sentencing comes amid heightened tensions between North Korea and the United States. Analysts have speculated North Korea could be using Bae as bait to get a high-profile American to visit the country.