Image copyright Reuters Image caption Otto Frederick Warmbier was taken to North Korea's top court

US student Otto Warmbier has been given 15 years hard labour in North Korea for crimes against the state.

Warmbier, 21, was arrested for trying to steal a propaganda sign from a hotel while visiting North Korea in January.

He later appeared on state TV apparently confessing and saying a church group had asked him to bring back a "trophy" from his trip.

North Korea sometimes uses the detention of foreigners as a means of exerting pressure on its adversaries.

The BBC's Stephen Evans in South Korea says the 15-year sentence is high compared to those given to foreigners in the past.

This could be due to the particularly high tensions at the moment between North Korea and the US, he says.

'Worst mistake'

North Korean state news agency KCNA said Warmbier was convicted under an article of the criminal code relating to subversion. The verdict was handed down by the Supreme Court.

Image copyright AFP Image caption Otto Warmbier said in February that he had made "the worst mistake of my life"

Warmbier, a student at the University of Virginia, was arrested on 2 January as he was trying to leave North Korea. He was accused of committing "hostile acts".

KCNA said at the time he had gone to North Korea "to destroy the country's unity" and that he had been "manipulated" by the US government.

At the end of February, at a tearful press conference in Pyongyang, he said he had "committed the crime of taking down a political slogan from the staff holding area of the Yanggakdo International Hotel".

"The aim of my task was to harm the motivation and work ethic of the Korean people. This was a very foolish aim," he was quoted as saying.

He said it was the "worst mistake" of his life.

North Korea detainees often recant their confessions once out of the country.

US tourism to North Korea is legal but the US State Department strongly advises against it.

Foreigners detained in North Korea

Other recent cases include:

Hyeon Soo Lim, a Canadian Christian pastor of South Korean origin, was sentenced to a life term of hard labour in December, for "crimes against the state".

Kim Dong Chul, a businessman who said he made frequent trips to the North's Rason Special Economic Zone, was arrested in October 2015 for "espionage". Pyongyang produced a passport that appeared to show he was a naturalised American.

Sandra Suh, an American aid worker, was arrested then expelled in April 2015, accused of gathering and producing anti-North propaganda.

Matthew Todd Miller was sentenced to six years' hard labour in September 2014 for what North Korean state media described as "hostile acts", but was released in November the same year.

Kenneth Bae was arrested in November 2012 and accused of using his tourism business to form groups to overthrow the government. Sentenced to 15 years' hard labour in May 2013 but was released along with Mr Miller.

Jeffrey Fowle, held for five months and charged with "anti-state" crimes, was released in October 2014.

Korean War veteran Merrill Newman, held in October 2013 on charges of "hostile acts", was released in December the same year.

The sentencing comes a day after veteran US diplomat Bill Richardson met North Korean officials at the UN in New York to try to push for Warmbier's release.

Mr Richardson has previously been involved in negotiations to secure the release of Americans from North Korea detention.

Human Rights Watch (HRW) condemned the sentence: "North Korea's sentencing of Otto Warmbier to 15 years hard labour for a college-style prank is outrageous and shocking" said Phil Robertson, deputy director of HRW's Asia division, in a statement.

North Korean state media took a less lenient view: "The accused confessed to the serious offense he had committed against the DPRK, pursuant to the US government's hostile policy toward it, in a bid to impair the unity of its people, after entering as a tourist," reported the KCNA news agency.

The Democratic People's Republic of Korea (DPRK) is North Korea's formal name.

Image copyright AP Image caption South Korea and US troops are currently engaged in their biggest ever military drills, a routine source of tension

North Korea has ramped up its hostile rhetoric in recent weeks, after the UN imposed some of its toughest ever sanctions.

The sanctions were a response to the North conducting its fourth nuclear test and launching a satellite into space, which was seen as a covert test of banned missile technology.

Pyongyang has also been angered by the US and South Korea carrying out their annual military drills, which this year involve some 315,000 personnel.

North Korea's leader Kim Jong-un has threatened "indiscriminate" nuclear attacks against the US and the South, and has said his country will soon test a nuclear warhead.

However analysts still doubt whether the North has the capacity to carry out a nuclear attack.