Libya's ex-ambassador to France, Omar Brebesh, has died in the custody of a militia from possible torture, less than 24 hours after he was detained by the armed group, Human Rights Watch said on Friday.
HRW said a Tripoli-based militia from the town of Zintan detained Brebesh on January 19 and that a preliminary autopsy found the cause of death included "multiple bodily injuries and fractured ribs."
"Photos of Brebesh's body, seen by Human Rights Watch, show welts, cuts and the apparent removal of toenails, indicating that he was tortured prior to death," the rights watchdog said in a statement.
It said a report by the judicial police in Tripoli also found that Brebesh had died from torture and that an unnamed suspect had confessed to killing him.
Brebesh, 62, served in the Libyan embassy to France from 2004 to 2008, first as cultural attache and then as acting ambassador for the last nine months of his term, the rights group said.
He continued to work with the Libyan foreign ministry under Kadhafi's regime during last year's uprising and as a lawyer in the ministry under the post-Kadhafi transitional government.
HRW said that an official at the Libyan foreign ministry told the group that he saw Brebesh at work 10 days before his death, and he appeared to be in good health.
The New York-based watchdog said that according to Brebesh's son Ziad the former ambassador had himself voluntarily submitted to an investigation by the Al-Shuhada Ashura militia in Tripoli.
On January 20 his family heard his body had appeared at a hospital in Zintan, about 100 kilometres (62 miles) southwest of the capital.
"I saw his face. There was blood on his nose and mouth. But I didn’t see the rest of his body or his face from the other side," HRW quoted Brebesh's other son Mohammed as saying.
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"There was a bump on his forehead. After that, I kissed him and that was it. Later, when we saw the other side of his face at the hospital in Tripoli, it looked like his jaw was broken, like his face was not in the right place."
Militias made up of former rebels who fought Moamer Kadhafi's forces have been facing growing criticism from rights groups for allegedly torturing prisoners, most of whom are loyalists of the slain dictator.
"The torture and killing of detainees is sadly an ongoing activity by some Libyan militias," Sarah Leah Whitson, Middle East and North Africa director at HRW.
"These abusive militias will keep torturing people until they are held to account. Libya’s leaders should show the political will to prosecute people who commit serious crimes, regardless of their role in the uprising."
Her comments come a week after Amnesty International and Doctors Without Borders reported "widespread torture" in prisons under the control of militias and of some officially recognised military.
The two groups said such cases were observed in the prisons of Tripoli, Misrata and smaller towns such as Ghariyan. Doctors Without Borders suspended its work in Misrata over these allegations.
On Thursday, Libyan Justice Minister Ali Hamida Ashur said the authorities would investigate all cases of "torture" in prisons and bring to justice those involved in it.
HRW said that a Zintan-based prosecutor has opened an investigation into Brebesh's death.
"The Libyan government should send a message that it will not tolerate torture and vigilante justice," Whitson said.
"The rule of law, and punishment for crimes, apply to all Libyans, including those who fought against Moamer Kadhafi."
Libya currently has about 8,500 detainees in about 60 facilities, majority of which are run by militias, rights group say.