A second Argentine judge has issued an international arrest warrant for former President Isabel Peron.
Isabel Peron has been living in Spain since 1981
Mrs Peron, who lives in Spain, faces extradition over alleged links to a right-wing paramilitary group which operated during her 1974-1976 rule.
The Anti-Communist Alliance, or Triple A, killed as many as 1,500 people in the 1970s, human rights groups say.
Mrs Peron, 75, was briefly detained in Madrid last week over the disappearance of a leftist student activist in 1976.
Federal Judge Norberto Oyarbide has ordered that Mrs Peron return to Argentina to answer questions about the government-linked death squad.
Investigators believe "Triple A" agents kidnapped and killed about 1,500 government opponents, including politicians, lawyers and journalists.
The BBC's Daniel Schweimler in Buenos Aires says what they would like to know is how much Isabel Peron knew, and whether she signed the orders for the killings.
Mrs Peron was arrested last week at her home in Madrid after a different judge issued an arrest warrant in connection with the disappearance of a student leader in 1976.
The Spanish authorities allowed her conditional release because of her frail health but said she would have to report to the police every 15 days.
A judicial source told Reuters news agency that Mrs Peron may be able to fight extradition on the basis of her dual Argentine and Spanish citizenship.
Correspondents say there is a push by the government of the incumbent President, Nestor Kirchner, to punish former members of the military regimes for their crimes.
Isabel Peron was the third wife of the three-times president of Argentina, Juan Domingo Peron. When he died in office in 1974, his widow took over.
Historians say she was an ineffectual leader, manipulated by her ministers at a time when Argentina was wracked by violence involving left-wing guerrillas and right-wing death squads.
She was removed in a military coup in 1976 and held under house arrest for several years before moving to Spain in 1981.
An estimated 30,000 people were killed, or "disappeared" from 1976 to 1983, during the military's repression of alleged left-wing opponents, which came to be known as the "dirty war".