Leftist Shining Path militants killed at least 18 people, including two children, in a remote region of Peru known for coca production and burned some of the bodies beyond recognition, the military said on Monday.
Pamphlets encouraging Peruvians to refrain from voting in the June 6 presidential election were found at the site of Sunday's massacre, according to a statement from the joint command of Peru's Armed Forces.
The military called the murders "an act of genocide" and said the Shining Path had previously labeled such attacks a form of "social cleansing." The statement assured Peruvians of "a secure electoral process."
The incident took place in a region called Valle de los Rios Apurimac, Ene y Mantaro (VRAEM), where 75 percent of cocaine is produced in the South American country, according to authorities.
"It is likely there will be more deaths," police commander Cesar Cervantes told RPP radio on Monday. Cervantes had earlier said that at least 18 had been killed.
The VRAEM, a mountainous region the size of Puerto Rico, is the centre of constant operations by the security forces against remnants of the Shining Path, which police allege acts as "bodyguards" for drug traffickers.
The Maoist rebel group, long regarded by the government as terrorists, launched one of the deadliest internal conflicts in Latin America in the 1980s. An estimated 69,000 people were killed, according to a truth commission.
The Shining Path began to fade in the early 1990s after the jailing of founder Abimael Guzman and has since morphed into a criminal group with ties to narco-traffickers.
Peru is slated to hold elections in less than two weeks, pitting socialist Pedro Castillo against conservative Keiko Fujimori.
The United Nations condemned "the murder" of the people and expressed its solidarity with the victims and their families.
"In the framework of the ongoing electoral process, we call on all actors to act responsibly, avoiding hate speech that increases tensions," said a statement from the UN office in Lima.
(FRANCE 24 with REUTERS and AFP)
