The search for Mr Nazar Haro was launched in December 2003

Miguel Nazar Haro is accused of ordering the killing of a suspected leader of a left-wing guerrilla group.

His arrest is the first by the prosecutor investigating Mexico's so-called "dirty war" against leftist activists during the 1960s and 1970s.

It comes over two months after warrants were issued against Mr Nazar Haro and two others for involvement in the case.

In December 2003, authorities launched a search for Mr Nazar Haro along with his predecessor as domestic spy chief, Luis de la Barreda and former police commander Juventino Romero.

He was arrested in the capital Mexico City and has now been flown to the north Mexican city of Monterrey, where he will face charges.

Correspondents say the arrest could mark a turning point in the campaign by President Vicente Fox to punish past atrocities.

A special prosecutor, Ignacio Carrillo, was appointed two years ago by Mr Fox's government to investigate and try abuses committed by state security forces in the 1970s.

Disappeared

The man who disappeared, Jesus Piedra, was abducted in Monterrey in 1975.

More than anything, more than prison, what we want is to know what happened to those who disappeared Rosario Ibarra, Mother of disappeared

He was the alleged leader of the 23 September League, which carried out several kidnappings and bank robberies in the 1970s to finance its revolutionary activities.

It was one of a number of small radical groups that operated in Mexico from the late 1960s to early 1980s.

The authorities fought back, allegedly using shadowy, often illegal methods which led to the deaths and disappearances of dozens of activists.

Piedra's mother, Rosario Ibarra, said many former state officials still should face charges - including former President Luis Echeverria, who held power from 1970-1976.

"Many people are calling to congratulate me. Why should I be congratulated when this is something the government should have done long ago?"