By Andrew Ward in Seoul

Published: February 2 2004 4:00 | Last Updated: February 2 2004 4:00

North Korea has killed political prisoners in gas chambers designed to test chemical weapons, according to an investigative documentary broadcast by Britain's BBC television yesterday.

A former North Korean prison officer described how entire families were put to death inside a glass chamber, as government scientists watched. The allegations were supported by what the BBC programme said were official North Korean documents confirming how prisoners were used to test chemical and biological weapons.

"I witnessed a whole family being tested on suffocating gas and dying in the gas chamber," said the former officer. "The parents were vomiting and dying, but till the very last moment they tried to save kids by doing mouth-to-mouth breathing."

The documentary, titled Access to Evil, represented arguably the most serious allegation of human rights abuses levelled against the secretive Communist state, which George W. Bush, US president, once named as part of an "axis of evil".

It was impossible to verify the BBC's claims independently or to contact the North Korean government about them, but Pyongyang has in the past denied abusing human rights.

Human rights groups have accused the international community of ignoring the country's brutal treatment of its 22m people as the world focuses instead on its pursuit of nuclear weapons.

Campaigners want the US and its partners to demand an improvement in North Korea's human rights as a condition of any deal to end its nuclear programme.

James Kelly, US assistant secretary of state, said yesterday he was "mildly optimistic" that a second round of six-party talks about the nuclear crisis would take place as early as this month.

Mr Kelly's comments came after he arrived in Seoul for talks with South Korean officials, in preparation for the expected six-way meeting, also involving North Korea, China, Japan and Russia.

North Korea has demanded economic assistance and a security assurance in return for scrapping its nuclear programme.

But critics have warned that any settlement that left Kim Jong-il, the country's leader, in power but failed to address human rights would allow the regime to continue terrorising its people.

More than 100,000 people are believed by human rights groups to be kept in prison camps in North Korea, many of them for dissent against Mr Kim's regime. Defectors have provided accounts of the camps, claiming that prisoners are subjected to torture, execution and forced abortions. Whole families are often imprisoned together if a single relative is found guilty of an offence.

"It is imperative that the international community does not continue to turn a blind eye to these atrocities," said Mervyn Thomas, chief executive of UK-based Christian Solidarity Worldwide.