Amnesty International on Friday expressed "grave concern" at the Bahraini authorities' repression of the political opposition, a day before the legislative elections.
"In the past two years, the political opposition has been detained, intimidated and silenced," said Devine Kenny, a senior UN investigator.
Amnesty's statement called on "the authorities to stop this ongoing and escalating repression and allow freedom of expression for dissenting voices, including those who oppose the monarchy."
"Bahrain's international partners and allies can not remain silent, and they must use their influence to pressure the authorities to comply with international standards," he said.
Citizens are heading to the polls on Saturday to elect a new parliament, in the absence of a real or competitive election campaign, after opposition authorities banned participation, in return for opposition supporters calling for a boycott.
The Shiite al-Wefaq Association and the secular Waad Association will not be able to participate in the elections after they were narrowed through a series of legal amendments approved by King Hamad bin Isa al-Khalifa.
The kingdom has been experiencing intermittent turmoil since a protest movement was suppressed in February 2011 in the midst of the Arab Spring, led by a Shi'ite majority whose leaders demand constitutional monarchy in the country ruled by a Sunni dynasty.