Argentina's last dictator Reynaldo Bignone, already serving a life term, was handed a 15-year prison sentence Thursday for rights violations at a clandestine detention center, sources said.

Bignone, 83, was given the extra time for his involvement in a detention center for leftist opponents. The "Chalet" on the grounds of a hospital near the capital was notorious as a holding place where detainees were allegedly tortured.

The former ruler had already been sentenced to life in prison, also for rights abuses committed under the country's 1976-83 military regime, and to 25 years behinD bars for "illegal privation of liberty and torture of the political prisoners."

Bignone became president of Argentina in 1982 after the country's humiliating defeat in the Falklands War, and turned over power the following year to democratically-elected president Raul Alfonsin.

Since amnesty laws were repealed in 2005, Argentine courts have convicted more than 200 leaders of the military regime, and cases have been opened against 800 former military and police officials.

Human rights groups estimate that as many as 30,000 people were killed or went missing during the regime, which waged a "dirty war" against the left.