HARBIN  -- Two officials in Northeast China's Heilongjiang province were sentenced to one year in prison on Thursday for dereliction of duty after a prisoner seduced and blackmailed a number of women while behind bars.

The two defendants stood trial at Longjiang County People's Court.

Wang Ge, former secretary of Nehe Prison's discipline inspection commission, and Liu Yang, an official with the prison's management unit, failed to supervise their subordinate staff and to carefully carry out relevant prison regulations, the court said.

Wang Dong, a prisoner who has been incarcerated since December 2012 at Nehe Prison, used the cellphone messaging app WeChat to chat with several women who lived near the prison and "established romantic relationships with them" during incarceration.

He extorted money from them by threatening to spread their nude videos and pictures. The blackmail came to light when one of Wang Dong's victims reported that she was being blackmailed to the police in late 2014.

The case has caused a public outcry about lax supervision in Chinese prisons.

Four former prison guards were handed jail terms from a year and four months to two and a half years in December last year.