More than one-third of Japan's prison population has been assaulted, intimidated or bullied by prison guards, the Justice Ministry's first extensive nationwide survey of inmates showed Monday.

The ministry sent questionnaires to 2,562 people -- prisoners doing time at three prisons as of July 4 and all inmates who were released between June 28 and July 4.

The survey results were submitted Monday to the Correctional Policy Reform Committee, an advisory panel. The committee, set up following two cases of fatal abuse of inmates at Nagoya Prison over the past two years, will propose reforms to human rights-related conditions, medical services and overall correctional programs at the nation's prisons by the end of this year.