North Korea, whose notorious prison camps have been condemned by global rights groups, announced Tuesday an amnesty for convicted criminals to coincide with the 70th anniversary of independence from Japanese colonial rule.

The pardons will take effect on August 1, the North's official KCNA news agency said, without specifying the number of criminals to be covered by the amnesty order.

Pardons will be extended to those "convicted of crimes against the country and its people", the news agency said, without elaborating.

Estimates of North Korea's prison population vary, but rights groups put it at around 200,000 men, women and children -- mostly held for political and not criminal reasons.

A comprehensive report published last year by a UN commission concluded that conditions in normal North Korean prisons were often every bit as harsh as those in the political gulag.

Many inmates are imprisoned without trial or any kind of due process, the report said, adding that beatings and sexual abuse of prisoners was commonplace.

KCNA said practical measures would be taken to "help the released people settle down" to a new life and work.

North Korea is currently holding four South Koreans charged with spying or illegal entry. None of them are expected to be included in the amnesty.

North Korea regularly offers pardons on major anniversaries -- most recently in 2012 to mark the 100th and 70th birth anniversaries respectively of late leaders Kim Il-Sung and Kim Jong-Il.

As well as the end of Japan's 1910-45 colonial rule over the Korean peninsula, this year also marks the 70th anniversary of the founding of the North's ruling Workers' Party of Korea.