A Peruvian judge has issued a new warrant for the arrest of former President Alberto Fujimori, who is living in exile in Chile.
Fujimori already faces corruption and human rights charges
It is alleged he ordered the killing of 20 members of the Maoist Shining Path rebel group during a 1992 prison riot.
Mr Fujimori is already wanted in Peru on charges of corruption and human rights abuses.
A Chilean judge said earlier this month an inquiry into an extradition request by Peru's authorities was closed.
He said he was likely to make a decision on the request before the end of the year.
This latest call for the detention of the former Peruvian president has been issued to Interpol amid fears that Mr Fujimori may try to leave Chile and flee to a country where he could be granted protection, says the BBC's Dan Collyns in Lima.
The deaths at the centre of the allegations were later presented as the result of a military operation to control a Shining Path mutiny in which 42 prisoners died in the Miguel Castro Castro jail.
But evidence shows most of the victims died of gunshot wounds to the head, suggesting that they were summarily executed.
The new charges come just days after Mr Fujimori said he did not know of the existence of a death squad - known as La Colina - before they carried out two massacres in the early 1990s which he has been charged with ordering.
He claims the death squad was formed during the first period in office of current President Alan Garcia between 1985 and 1990, an allegation which Mr Garcia has rejected.
Mr Fujimori, who led Peru between 1990 and 2000, was arrested when he unexpectedly arrived in Chile last year, having spent the previous five years in Japan.
He holds Japanese citizenship through his parents.
Meanwhile in Peru, political pressure is building to ensure that the former president is returned to face justice, our correspondent says.