Between June 2016 and June 2017, at least 169 Bahrainis have also been threatened, harassed, and banned from leaving the Gulf island nation, Amnesty International,  said.
"We have heard horrific allegations of torture in Bahrain. They must be promptly and effectively investigated and those responsible brought to justice," said Philip Luther, Amnesty's research and advocacy director for the Middle East and North Africa. 
"The government of Bahrain has managed to crush a formerly thriving civil society and reduced it to a few lone voices who still dare to speak out."
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One of the victims, prominent human rights defender Ebtisam al-saegh, said.
she was blindfolded, beaten, and sexually assaulted while in the custody of the National Security Agency.
"They took away my humanity," Saegh told researchers. 
An "all-out campaign" was launched to dismantle the main opposition Al-Wefaq Party, Amnesty said. 
A prominent Shia cleric, Sheikh Isa Qassin, was stripped of his citizenship, and dozens of his followers were detained for demonstrating.
Bahrain's Ministry of Interior was asked for comment, but none was received by publication time.
Michael Payne, international advocacy officer at the Washington-based Americans for Democracy and Human Rights in Bahrain, confirmed the 169 figure cited by Amnesty. He told Al Jazeera in total there are 3,500 to 4,000 political prisoners languishing in Bahraini prisons.