Otto Warmbier, a 21-year-old from the University of Virginia, admitted on Monday to stealing a political banner while on tour in the North Korean capital.

A sobbing Warmbier confessed to the crime on North Korean state television, saying he had made "the worst mistake of my life."

According to a statement issued during a press conference, the American said he had stolen the banner to give to a family friend back in the States who wanted it as a "trophy." That friend - a member of the detainee's church in Ohio - had promised a car and a payment of $200,000 ($182,000) to his family in return for the gift, Warmbier said during his confession.

An 'inexcusable' arrest

Warmbier was arrested in January after traveling to North Korea as part of a guided tour hosted by a China-based company called Young Pioneer Tours. Upon his detainment, Pyongyang accused the American of "tacit connivance of the US government and under its manipulation."

The country's media hadn't yet released details of what charges or punishment Warmbier faces.

Ohio Governor John Kasich, who is currently running for president, called the arrest "inexcusable" and called on Pyongyang to show proof of the student's alleged crimes.

Tension on the peninsula

The arrest comes as Washington prepares to ramp up sanctions against Pyongyang in return for the communist country's recent nuclear tests.

US Ambassador to the UN Samantha Power submitted a draft resolution of the sanctions to the UN Security Council last week.

North Korea set off alarm bells around the world when it tested a hydrogen bomb in early 2016, followed by the launch of what it claimed was a satellite-bearing rocket, but is widely believed to have been a ballistic missile test.

blc/kms (AFP, AP)