The Supreme Court overturned its own ruling at the request of the Inter-American Court of Human Rights.
Announcing the decision on Thursday night, court President Cesar San Martin also said an arrest warrant had been issued for Alberto Pinto, the former army intelligence chief released after the July ruling. He had been serving 15 years for aggravated murder.
The earlier ruling had provoked widespread outrage in Peru. Most of the 15 had seen their sentences reduced from 25 to 20 years, rendering about half eligible to apply for parole.
The men belonged to the so-called Colina death squad created under then-spy chief Vladimiro Montesinos