Montesinos, former armed forces chief Juan Hermoza Rios, army chief Julio Salazar Monroe and Major Santiago Martin Rivas were jailed for 25 years in 2010 for ordering the Colina Group to kill 24 people in massacres in 1991 and 1992.

The Supreme Court reduced the sentences of Montesinos, Hermoza and Salazar to 20 years, and also cut the term of Rivas, who led the death squad, to 22 years, said Javier Villa Stein, chairman of the Supreme Court's criminal chamber.

The killings were conducted during Peru's so-called dirty war in the 1990s, during Fujimori's 10-year fight against the leftist Shining Path guerrillas, in which atrocities were committed by both sides.

Other unnamed members of the Colina Group had their sentences cut from 20 years to 17 years, said Stein, who stated that the hit squad's crimes "were against human rights but not part of a widespread attack against civilians."

Montesinos was Fujimori's intelligence chief. He was privy to government policies and strategy in its campaign against the Shining Path.

Fujimori, who served as Peru's president from 1990 to 2000, was sentenced in 2009 to 25 years in prison for his role in the death squad's killings.

His family have repeatedly asked that he be pardoned due to his poor health.