The UN human rights office has criticised the harsh sentences given this week to anti-government protesters and medical staff in Bahrain.

A spokesman for the UN High Commissioner for Human Rights says the fact that the sentences were handed down by "a military court with serious due-process irregularities raises severe concerns."

Rupert Colville told reporters in Geneva on Friday that the Bahrain government has a duty to ensure that all detainees are charged with recognisable criminal offenses.

Bahrain's special security court on Thursday sentenced a protester to death for killing a policeman. It also gave doctors and nurses who treated injured protesters during the country's uprising earlier this year lengthy prison sentences.