LIMA, Peru—Peru's Supreme Court has reduced the murder sentence of former spy chief Vladimiro Montesinos along with the sentences of 15 members of a military death squad also convicted in the killings of 25 people in 1991 and 1992.

President Ollanta Humala criticized Friday's decision and his justice minister, Juan Jimenez, called it "an embarrassment for the country."

The court's decision, which is not subject to appeal, reduced the sentence for Montesinos from 25 to 20 years. The panel also ordered former military intelligence chief Alberto Pinto freed immediately. He had been sentenced to 15 years in 2010.

The court ruled that the killings, including of an 8-year-old boy, did not amount to crimes against humanity but rather murders.