By Marco Aquino

LIMA (Reuters) - Prosecutors in Peru are investigating whether a group of police extrajudicially killed 27 people in a scheme to earn promotions and rewards from superiors by appearing to stop dangerous criminals, a source said on Monday.

The inquiry was opened earlier this year after the interior ministry sent public prosecutors a report on what it said may be a criminal ring with dozens of police officers involved in killings between 2012 and 2015, the source in the attorney general's office said.

Prosecutors suspect the officers ordered undercover informants to set up kidnappings and robberies with suspected criminals in order to catch and kill them under the pretense of legitimate uses of force, said the source, who spoke on condition of anonymity.

The investigation was first revealed Sunday by the local investigative news show Cuarto Poder on America Television.

The source said Attorney General Pablo Sanchez escalated the inquiry to a higher priority and authorized broader powers for the lead prosecutor on Monday.

The case puts more pressure on President Pedro Pablo Kuczynski, who took office on Thursday, to reform a police force widely viewed as corrupt while meeting popular demands for tougher treatment of criminals.

Kuczynski's interior minister, Carlos Basombrio, said on Cuarto Poder that he would publish a report on the case within 10 days.

Daniel Urresti, an interior minister in the government of former President Ollanta Humala, said in broadcast comments that he had been aware of the inquiry and urged Peruvians not to jump to conclusions.

The report by Cuarto Poder included the testimony of a businessman identified as Jose Candiote, who said that four men who kidnapped him did not resist arrest, even though police said the men were killed in a shootout. Candiote said he was handcuffed and left alone in the room of an abandoned house before he heard gunshots in an adjoining room.

(Reporting By Marco Aquino, Writing by Mitra Taj; Editing by David Gregorio)