North Korea has sentenced a South Korean-born American citizen to 10 years of hard labor for subversion and espionage, a North Korean official told CNN. Prosecutors were seeking a 15-year hard labor sentence for Kim Dong Chul for committing “offenses in a scheme to overthrow the socialist system of the DPRK,” according to state-run news agency KCNA. The defense asked that Kim’s sentence be commuted, arguing “the crimes by the accused are very serious but he is old and may repent of his faults.” Friday’s verdict was handed down by North Korea’s Supreme Court. The U.S. State Department said it is aware of the media reports about Kim’s sentence. “The welfare of U.S. citizens is one of the Department’s highest priorities,” State Department spokesman John Kirby said in an emailed statement. “In cases where U.S. citizens are reported detained in North Korea, we work closely with the Swedish Embassy, which serves as the United States’ Protecting Power in North Korea. We have no further comment due to privacy considerations.” Kim is the second American to receive a hard labor sentence from North Korea in the past two months. In March, University of Virginia student Otto Frederick Warmbier was sentenced to 15 years of hard labor for allegedly removing a political banner from a Pyongyang hotel. CNN’s Will Ripley spoke to Kim in January, under the watch of North Korean officials. Kim told CNN he used to live in Fairfax, Virginia, and had been in detention for three months. Exclusive: North Korea reveals U.S. prisoner to CNN Kim said he moved to Yanji, a Chinese city near the Chinese-North Korean border that acts as a trade hub between the two countries, in 2001. From Yanji, Kim said he commuted daily to Rason, a special economic zone on the North Korean side of the border, where he served as president of a company involved in international trade and hotel services. Spying confession According to Kim, he spied on behalf of “South Korean conservative elements” on the country’s nuclear and military program. “I was tasked with taking photos of military secrets and ‘scandalous’ scenes,” he said at the time. “They asked me to help destroy the (North Korean) system and spread propaganda against the government.” North Korea launches two midrange missiles; both tests fail Kim’s comments to CNN in January were made in the presence of North Korean officials and CNN cannot determine whether they were made under duress. Like Kim, the University of Virginia student Warmbier also gave a confession to international media. North Korea accuses Warmbier of taking the banner at the urging of a church member, the CIA and a secretive university organization. North Korea ‘collecting assets’ The detainment of Americans and other foreign citizens is interpreted by North Korea watchers as the collection of bargaining chips. “It shows anyone or anything can be used as political, military or economic leverage,” said Jasper Kim, director of Ewha University’s Center for Conflict Management. “I think the strategy by DPRK is to collect possible assets for leverage and basically, playing a game of geopolitical poker, unveiling cards strategically when they have the most value,” he said, using an abbreviation for North Korea. Kim, who was detained last October, was only revealed to have been held in January. He was sentenced a day after North Korea carried out two provocative – but apparently failed – missile tests. “The beginning of the year is particularly strategic, typically a lot of things happen at that point: the joint military exercises between U.S. and ROK (South Korea), that occurs and this year in particular, Worker’s Party congress which hasn’t happened since 1980,” Jasper Kim said. What is the Worker’s Party congress and why does it matter? The “DPRK is definitely getting more aggressive, more erratic,” he said.