Inside a once-secret detention center where political dissidents were tortured and killed during Argentina's dictatorship 25 years ago, forensic anthropologists have discovered a pit containing 10,000 bone fragments.

The first discovery of human remains inside a detention center confirms the testimonies of hundreds of survivors who have said for years that authorities tortured, killed and burned the bodies of political opponents, they said Tuesday.

"This scientifically confirms the testimonies of the detained," said Luis Fondebrider, a forensic anthropologist who helped uncover the remains inside the former detention center in La Plata known as Arana.

The 10,000 bone fragments were unearthed between February and September, and on Tuesday Fondebrider and his team announced that the remains were human. Now months of laboratory work is needed to determine even the minimum number of bodies that were destroyed in the pit.

But the evidence already shows that bodies were thrown into the pit, covered in fuel and burned along with tires, to mask the smell of burning flesh. More than 200 bullet marks were found along a wall bordering the mass grave.

The bones weren't completely reduced to ash, allowing for genetic analysis to identify the dead. But Fondebrider cautioned that it won't be possible to identify many of the victims, since prolonged exposure to fire destroys most DNA.

"This is the first time there is proof that Arana wasn't only a detention and torture center, but also a center of elimination," said Maria Vedio, 47, legal chair for the Permanent Assembly for Human Rights La Plata.

Some supporters of the military dictatorship have denied that detainees were tortured or killed, despite the well-documented toll from the "dirty war" crackdown in which political opponents of the junta were made "to disappear," along with their spouses, children, and other innocent people unlucky enough to appear in their address books.

Official records put the number of disappeared at 13,000, while human rights groups 30,000 were killed.

Much of the evidence disappeared as well — their bodies were thrown into the sea from airplanes in so-called "death flights," while others were buried or burned in mass graves far from detention centers.

The confirmation of human remains at Arana rebukes any efforts to deny this history, Vedio said.

The military and police operated about 10 detention centers during the 1976-1983 dictatorship in La Plata, a city of universities south of Buenos Aires where the crackdown's toll on college students was particularly severe.

The Argentine Forensic Anthropology Team has identified 350 bodies in Argentina over more than two decades.

At least 14 former Argentine state security agents and their civilian allies have been found guilty of human rights crimes, including forced disappearances and kidnapping. Another 358 are awaiting trial, according to the Buenos Aires-based Center for Legal and Social Studies.