A judge in Mexico has issued a warrant for the arrest of former President Luis Echeverria on genocide charges.
Echeverria was interior minister at the time of the killings
A judge ordered the arrest of Mr Echeverria, 84, over the killing of up to 300 students in Mexico City in 1968.
The latest ruling in a long-running affair came just four months after a court dismissed the charges, saying the killings happened too long ago.
Mr Echeverria was interior minister when troops opened fire on protesters days before the Olympic Games opened.
In July, a judge ruled that the events of 2 October 1968 fell outside Mexico's 30-year statute of limitations, ruling out a trial.
But prosecutors successfully argued that Mr Echeverria had effective immunity until he left office on 1 December 1976, and the statute should be considered from that date.
Because of his age, Mr Echeverria would be likely to face house arrest, but there was no confirmation whether the warrant would be used immediately.
He was originally placed under house arrest in June, but released after the July ruling.
Juan Velazquez, a lawyer for Mr Echeverria, said he would appeal against the latest decision.
Mr Echeverria was interior minister in 1968 at the time of the killings in Tlatelolco Square in Mexico City.
Human rights activists say up to 300 people were killed in the shootings, although officials said the death toll was just 30.
Mr Echeverria denies allegations that he posted snipers on scores of buildings and gave orders to shoot anti-government protesters, and disputes that the deaths on 2 October 1968 constitute genocide.
Mr Echeverria was president from 1970 to 1976 during which hundreds of people died or disappeared during the "Dirty War" on leftists.