The White House has called for the "immediate release" of a 21-year-old US student who was handed an "unduly harsh" sentence of 15 years hard labour in North Korea. Otto Warmbier had travelled to Pyongyang on a trip organised by a China-based travel company and was arrested for trying to steal a propaganda sign from a hotel in January.

The Virginia University student was found guilty after a one-hour trial in the isolated country's Supreme Court on 16 March under an article of the criminal code relating to subversion.

A church in the US state of Ohio had allegedly offered Warmbier a car worth $10,000 (£7,200) if he managed to smuggle a propaganda poster out of the isolated country. He was arrested after trying to steal the poster at the Yanggakdo International Hotel based in the capital of Pyongyang and taken into custody.

It is not unusual for Kim Jong-Un's dictatorship to detain foreigners in exchange for political leverage. In a tense international climate where angry rhetoric and ballistic missile launches by the North Koreans have been met with harsh sanctions from the UN and the US, it is possible that American negotiators could arrange a release for the Warmbier.

Hours after the sentence was announced, a White House spokesman accused the Democratic People's Republic of Korea (DPRK) of using US citizens as "pawns to pursue a political agenda". "We strongly encourage the North Korean government to pardon him and grant him special amnesty and immediate release," White House spokesman Josh Earnest said to the BBC.

US State Department spokesman Mark Toner said that the punishment does not fit the alleged crime and was "unduly harsh". Some foreigners have been released shortly after convictions and have revealed their so-called "confessions" were extracted under pressure.

Warmbier had earlier confessed to committing the crime on DPRK national television. "I committed the crime of taking down a political slogan from the staff holding area of the Yanggakdo International Hotel. I apologise to each and every one of the millions of the Korean people and I beg that you see how I was used and manipulated," he said on 29 February.

"My reward for my crime was so much smaller than the rewards that the Z Society and the Friendship United Methodist Church get from the United States Administration," he added.

Other Americans captured and released by North Korea include:

American aid worker Sandra Suh was arrested and accused of gathering and producing anti-DPRK propaganda. She was expelled in April 2015.

In September 2014 Matthew Todd Miller was handed six years hard labour for what Pyongyang described as "hostile acts", but was released a few months later in November.

Evangelical Christian missionary Kenneth Bae was arrested in November 2012 and accused of using a tourism business to form groups that planned a coup. He was sentenced to 15 years hard labour in May 2013 but was released along with Miller.