Seoul, March 17 The US today accused North Korea of jailing an American student for political reasons and called for his immediate release after Pyongyang sentenced him to 15 years’ hard labour for stealing a propaganda sign from a hotel. Otto Warmbier, a 21-year-old student from the University of Virginia, was convicted of subversive activities and sentenced by North Korea’s Supreme Court, the North’s official KCNA news agency said. White House spokesman Josh Earnest charged that North Korea was using US citizens as “pawns to pursue a political agenda” and urged it to free him. “We strongly encourage the North Korean government to pardon him and grant him special amnesty and immediate release,” said Earnest. “The allegations for which this individual was arrested and imprisoned would not give rise to arrest or imprisonment in the United States or in just about any other country in the world.” Observers said the harsh sentence was likely a reflection of soaring military tensions on the divided Korean peninsula following the North’s nuclear test in January and long-range rocket launch a month later. The United States took a leading role in securing the resulting sanctions that the UN Security Council imposed on the North earlier this month. In recent weeks Pyongyang has maintained a daily barrage of nuclear strike threats against both Seoul and Washington, ostensibly over ongoing large-scale South Korea-US military drills that the North sees as provocative rehearsals for invasion. In announcing the jail sentence, KCNA said Warmbier had committed his offence “pursuant to the US government’s hostile policy” towards North Korea.