Bahrain has sentenced 13 "political prisoners" to three more years in jail over a 2021 protest against the conditions in which they were held, a rights group said Wednesday.
The prisoners were sentenced "in a mass trial amid credible torture allegations", the London-based Bahrain Institute for Rights and Democracy (BIRD) said in a statement.
The court announced a verdict on Tuesday against 65 defendants, none of whom were present at the session, the group said, adding that "62 of them are political prisoners".
On top of the sentences they were already serving, the judges sentenced 13 men to three more years in prison, and acquitted 52 others, BIRD said.
It denounced "severe due process violations, including the right to attend the trial, or meeting with the lawyer".
The events over which they were convicted date back to 2021 when hundreds of inmates protested their conditions, including the lack of medical care amid the Covid-19 pandemic, in Bahrain's notorious Jau prison.
Last month, dozens of prisoners -- 121 according to authorities -- launched a hunger strike, once again protesting the conditions at the same prison.
They suspended their strike in mid-September after the government made commitments to improve their situation.
"Victims of torture are condemned while torturers avoid any accountability," said Sayed Alwadaei, advocacy officer at BIRD, in the statement.
The Gulf island kingdom is regularly accused by rights groups of serious human rights violations targeting members of the opposition, particularly since the violent repression of mass protests in 2011 in the wake of the Arab Spring uprisings.
Bahraini authorities on Wednesday assured that the prisoners' legal rights are guaranteed and said the legal proceedings were "carried out in accordance with due process".
"The incident in question, which occurred at Jau Prison on 17 April 2021, was a pre-meditated violent attempt by a small but well-organised group of inmates to disrupt the facility's operations," prison authorities wrote to AFP.
According to them, "the incident was categorically not a peaceful sit-in or protest" and "the facility's staff took proportionate measures".
In the wake of the 2021 prison protest, the United Nations had voiced its concern about "unnecessary and disproportionate force" targeting "a peaceful sit-in" at the facility.
The sit-in was motivated by the death of an activist, resulting from inadequate medical care, according to other prisoners.