By Daniel Schweimler BBC News

President Fox appointed a special Dirty War investigator

The move clears the way for the possible arrest and prosecution of former officials implicated in the kidnappings of left-wing activists in the late 1960s and '70s.

The country's highest court ruled unanimously that the statute of limitations did not apply to the 1975 kidnapping of the alleged rebel, Jesus Piedra, overturning an earlier decision by a lower court.

The ruling has been welcomed by politicians and human rights groups in Mexico and abroad.

The Supreme Court said the statute of limitations did not apply since Mr Piedra's body has never been found and the investigation is still open.

A spokesman said a lower court must now decide whether to arrest two former police officers who commanded the now defunct Federal Security Directorate.

The ruling appears only to apply to kidnappings and does not cover other political crimes.

Praise

But human rights activists have welcomed it.

The paths to justice are opening - slowly, but they're opening Human rights activist

"The paths to justice are opening," said one activist. "Slowly, but they're opening."

A former political prisoner, Felix Hernandez, said: "This establishes an important precedent. We are now in a position to take the next step."

The disappeared man, Jesus Piedra, was abducted in the northern Mexican city of Monterrey.

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, using shadowy, often illegal methods which led to the deaths and disappearances of dozens of activists.

There has been growing pressure in Mexico to investigate the abuses committed during what has become known as the country's Dirty War.