Fiji’s police, corrections officers and military personnel consistently use torture against people accused of crimes or in custody, a new report from Amnesty International says.

The report, launched in Suva on Monday, details beatings, rape, sexual violence, attack by police dogs and even murder being used by security forces with impunity.

Security forces who commit human rights abuses rarely face sanction – Fiji’s current constitution entrenches immunities for any government action between 2006 and 2014 – and even when security officials are convicted of crimes, they are often quickly pardoned and released from prison, the Amnesty report says.

At least five people have been beaten to death in police or military custody in Fiji since the 2006 military coup, including 19-year-old Sakiusa Rabaka who was beaten, sexually assaulted and forced to perform military exercises in January 2007. He died from his injuries on a military base in Nadi. Eight police officers and one military officer were ultimately convicted over his death and sentenced to prison terms. All were released within a month.

In August 2014, robbery suspect Vilikesa Soko died, four days after being arrested, from a blood clot on his lungs after a sustained physical and sexual assault. His autopsy showed multiple traumatic injuries, including to his rectum and penis.

Police have also been accused of torturing suspects in order to obtain confessions, including by rubbing chillies on to people’s bodies, pouring water in their ears, or dropping large rocks on their backs.

Videos of police assaults on civilians have been circulated on social media, including footage shot in November 2012 showing one half-naked man being beaten and sexually assaulted by police and military officers, while another man has a police dog set upon him.

In a video clip circulated online from October this year, three police officers are shown beating suspects on the side of the road.

Kate Schuetze, Amnesty International’s Pacific researcher, said that in Fiji “accountability for torture is the exception rather than the rule”.

“This amounts to a climate of near impunity,” she said. “It is the result of the fact that torture is poorly defined in law, immunity is granted, there are few legal safeguards and there is no independent oversight.”

The Amnesty report calls for independent oversight of Fiji’s security forces, the reform of the country’s legal framework and the bringing of officials responsible for torture to justice.

“To rid Fiji of torture, the authorities should withdraw the armed forces from policing tasks and the military should not be above the law,” Schuetze said.

“Not only do the security forces know that torture is taking place, they have stood in the way of accountability. While the Fijian authorities have ratified the UN convention against torture and pledged to end this cruel practice, this will remain an empty gesture until decisive action is taken.”

Fiji’s prime minister, Frank Bainimarama, the former military commander who came to power in the 2006 coup, has acknowledged the systemic violence within the country’s security apparatus, which plays a prominent role in the country’s politics.

Speaking to the UN’s regional conference on the convention against torture in October, he conceded: “This culture of what we call the buturaki – the beating – is deeply ingrained in parts of the Fijian psyche.

“We have long had a culture in Fiji of people resorting to violence. Whether it is against women in the home, instilling discipline in our children or the police attempting to extract confessions from criminal suspects.”

But he said such violence was unacceptable in the modern age and that his government had imposed a “zero tolerance” policy for torture and other human rights abuses.

“We do not have – and never have had – a state-sanctioned policy of torture in Fiji,” he said.

“What we have had are occasional problems with individuals or groups of people taking the law into their own hands and violating the human rights of others. But ... no act of torture or cruel, inhuman or degrading treatment has been sanctioned by the state.”

Fiji was criticised at the UN’s Universal Periodic Review – where countries’ human rights records are assessed by other nation states – over its “culture of abuse of power”. The Pacific Islands Forum briefly suspended Fiji over human rights abuses.

Bainimarama accused the countries critical of Fiji of hypocrisy, singling out the US, which has had a fraught post-coup relationship with the Pacific archipelago nation, and Australia, its largest regional neighbour.

“In the case of the United States and Australia ... these have been state policies – a deliberate course of action taken by democratically elected governments,” he said. “America using an acknowledged method of torture to combat terrorism, Australia detaining innocent people in cruel, inhumane or degrading circumstances to protect the integrity of its borders.”