North Korea's Supreme Court on Sunday sentenced US citizen Matthew Miller to six years' hard labour for "hostile" acts, two weeks after he and two other detained Americans had pleaded for help from Washington.

Miller becomes the second American serving a hard labour prison term in the North amid accusations that Pyongyang is using them to extract political concessions from Washington.

The 24-year-old was arrested in April after he allegedly ripped up his visa at immigration and demanded asylum.

"He committed acts hostile to the (North) while entering the territory of the (North) under the guise of a tourist last April," the state-run KCNA news agency said in announcing Sunday's court ruling.

Pictures published by KCNA showed a sombre-looking Miller, dressed in a black polo neck and black trousers, sitting and standing in the courtroom dock, flanked by two uniformed guards.

A photo of the evidence table showed what appeared to be Miller's ripped-up visa, as well as his US passport, a tablet computer and a smartphone.

- Plea for help -

The verdict came after Miller and the two other US detainees, Kenneth Bae and Jeffrey Fowle, pleaded for Washington's help in a televised interview with CNN in Pyongyang.

"My situation is very urgent," Miller told CNN.

"I think this interview is my final chance to push the American government into helping me," he added.

Bae, a Korean-American described by Pyongyang as a militant Christian evangelist, was sentenced last year to 15 years' hard labour on charges of seeking to topple the North's regime.

Fowle entered the North in April and was detained after reportedly leaving a Bible at a hotel. His trial has been announced but no date has been set.

Washington has vowed to "leave no stone unturned" in efforts to free the trio and repeatedly urged Pyongyang to release them.

Analysts say Miller's trial is part of Pyongyang's wider efforts to capture US attention and force it to the negotiating table.

"The North probably knows the US is too busy with bigger crises in the Middle East and other regions," Professor Yang Moo-Jin of Seoul's University of North Korean Studies told AFP.

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"But what else does the North have? This so-called 'detainee diplomacy' seems to be the only leverage left for them to catch US attention," he said.

- High-level US visit? -

Washington has no diplomatic relations with Pyongyang and, in the past, North Korea has released detained Americans after visits by former presidents Bill Clinton and Jimmy Carter.

The US special envoy for North Korean human rights issues, Robert King, has twice tried to visit the North to secure Bae's release, only for Pyongyang to cancel at the last minute.

North Korea has, in recent months, sought to push the United States into agreeing to resume six-party talks on the North's nuclear programme, but Washington insists Pyongyang must first show a tangible commitment to denuclearisation.

"Even if a high-level visitor goes to North Korea, it is unlikely that the Obama administration will allow the occasion of the visit to broaden the conversation to include nuclear issues," said Scott Snyder, director of US-Korea policy at the Council on Foreign Relations.

Miller's trial was held a day after North Korea published a 53,000 word rebuttal of the "distorted views" in a report by a special UN human rights commission six months ago -- which listed violations so severe as to amount to crimes against humanity.

The rebuttal compiled by the North's Association for Human Rights Studies insisted that its people enjoyed "genuine human rights" and that "serious misunderstandings" had arisen because of fabricated reports originating from hostile nations like the United States.

In its report issued in February, the UN Commission on Inquiry into the North's rights record detailed a wide range of systemic abuses including murder, enslavement and torture.

The commission, which interviewed survivors of the North's notorious gulag system and many other defectors, concluded that many of the violations constituted crimes against humanity, and suggested they could be placed before the International Criminal Court.

"The gravity, scale and nature of these violations revealed a state that does not have any parallel in the contemporary world," it said.

The rebuttal published Saturday by the North said the UN report was based on the "testimonies of human scum who betrayed their homeland and people."