The report, released by Human Rights Watch (HRW), found that the country's security forces have continued with the same forms of abuse that the Bahrain Independent Commission of Inquiry (BICI) documented in the violent crackdown on protesters in 2011.
The 2011 BICI report concluded that the National Security Agency and the Interior Ministry "followed a systematic practice of physical and psychological mistreatment, which in many cases amounted to torture, with respect to a large number of detainees in their custody".
Researchers said that Bahrain has fundamentally failed to implement the recommendations made by the Commission in 2011, with the country's key western allies, such as the UK, accused of turning a blind eye to abuses.
"The claims of Bahrain and its allies that authorities have ended torture in detention are simply not credible."
"All the available evidence supports the conclusion that these new institutions have not effectively tackled what the BICI report described as a 'culture of impunity' among security forces," Joe Stork, HRW's deputy Middle East director said.
Electric Shocks, Extreme Cold, Sexual Abuse
The HRW report is based on interviews with 10 detainees who said they experienced interrogations at the Bahraini Interior Ministry's Criminal Investigations Directorate (CID) and in police stations since 2012, while the findings also drew on the testimonies of four former inmates of Jaw prison, who said they had been tortured in March 2015.
All of those questioned by HRW said that authorities had physically assaulted them, with many subjected to electric shocks, being suspended in painful positions, while handcuffed and exposed to extreme cold.
Among other shocking alleged incidents, one former detainee said CID officers beat his penis with a hose before forcing several fingers into his anus.
Others were threatened with rape, while one victim accused officers of threatening to rape his wife.
There are also concerns over the attitude of officers involved in Bahrain's security services, with some officials boasting about their reputation to inflict pain on detainees.
"I'll show you why Wifaq [Bahrain's leading opposition party] calls Bahrain the capital of torture," one former detainee quoted an interrogator as telling him. Another said a CID officer held something to his nose and told him it was "the blood of people who don't cooperate".
Pressure on Britain, US
The report's findings raise serous questions over the legitimacy of Bahrain's relationship as a key ally to western nations such as the US and UK.
Britain has been one of Bahrain's staunchest defenders, arguing that although the situation in the country is not perfect, Bahrain has been reforming its security forces and accountability mechanisms. However HRW refutes this, and has called for the UK to scrap funding for security service reform.
The findings also come just weeks after UK Foreign Secretary Philip Hammond inaugurated a highly controversial new British naval base near the Bahraini capital of Manama.
Other recommendations urge the US to impose restrictions on arms sales until human rights improvements are made, while HRW believes there needs to be an overhaul of Bahrain's security services.
"Since the peaceful anti-government protests of 2011, which the authorities responded to with brutal and lethal force, the Bahrain government has overseen a campaign of incarceration that has decimated its pro-democracy movement," Stork said.
"Bahrain can't claim any progress on torture while its anti-torture institutions lack independence and transparency and until it takes some serious steps to address the complete lack of accountability for the abuse of detainees."