Retired Gen. Gregorio Alvarez, who headed Uruguay's civilian-military regime from 1981 to 1985, died Wednesday in Montevideo, officials told EFE. He was 91.

Alvarez, convicted and sentenced in 2009 to 25 years in prison on 37 counts of murder and human rights violations, had been admitted to a hospital several weeks ago with serious health problems.

In mid-2015, Alvarez suffered a stroke. Earlier this month, he had a heart attack and was taken to the Armed Forces Central Hospital, where he died.

Alvarez, the son and grandson of generals, entered the National Military Academy in 1940 and graduated as a cavalry officer.

After Uruguayans rejected constitutional reforms drafted by the armed forces in a 1980 referendum, most high-ranking officers abandoned Alvarez, who wanted to continue military control.

Alvarez started talks with the political parties, leading to elections in 1984 and Julio Maria Sanguinetti taking office as president.

The retired general was one of the individuals being prosecuted in Italy for their role in "Operation Condor," an international campaign among 1970s South American military regimes that coordinated the cross-border detention, torture and summary execution of suspected leftists.

Operation Condor consisted of intelligence sharing between the dictatorships of the Southern Cone for the purpose of hunting down and exterminating leftists in Argentina, Bolivia, Brazil, Chile, Paraguay and Uruguay.

Human rights groups estimate that Operation Condor resulted in the deaths of hundreds if not thousands of people in Latin America.