Relatives of Laura Ling and Euna Lee were speaking to CNN after the communist state's official media gave its first details of their alleged crimes.

Border guards detained the TV reporters on March 17 along the frontier with China while they were researching a story about the plight of refugees fleeing the North.

A court on June 8 sentenced Ling, 32, and Lee, 36, to 12 years of 'reform through labour' for an illegal border crossing and an unspecified 'grave crime'.

Late on Tuesday North Korea's official news agency said the pair had admitted a politically motivated 'smear campaign' against Pyongyang over human rights issues.

It said they were 'prompted by the political motive to isolate and stifle' the North's system 'by faking up moving images aimed at falsifying its human rights performance and hurling slanders and calumnies at it'.

Laura's sister Lisa, herself a journalist, told CNN she hoped Pyongyang 'now will show compassion and just let them come home'. The pair are journalists and 'were doing their job", she said, expressing fears about their mental state.

Euna Lee's husband Michael Saldate said their four-year-old daughter Hannah still asks: 'Is mommy coming home soon?' 'I just say (to her), keep your hope up,' Mr Saldate said in the interview.

US officials led by Secretary of State Hillary Clinton have appealed to the North for clemency on humanitarian grounds and said the case should not be linked to the ongoing nuclear standoff.

Relations between the North and the US and its allies are at their worst for years following Pyongyang's second nuclear test on May 25 and subsequent UN sanctions. -- AFP