A prison governor in northern Poland has stabbed an inmate to death, the head of the country's penitentiary said today.

The governor, who was identified only as Andrzej G., attacked his victim during an inspection Sunday at the prison in Sztum, northern Poland, Jacek Wlodarski told rolling news channel TVN24.

The dead man was identified as Jozef S., who was serving a lengthy sentence and due for release in 2030.

He had made regular written complaints about his conditions of detention.

The governor stabbed the inmate at least four times when he was inspecting his cell.

Investigators said they were focusing on two possible motives: either a conflict between the two men, or that the governor had personal problems.