A former colonel in the Guatemalan army has been found guilty of ordering the murder of an anthropologist whose research exposed crimes during the country's civil war.

Myrna Mack was stabbed to death aged 39 outside her office in Guatemala City in 1990, and a junior officer had been found guilty of her murder in 1993.

Thousands died in Guatemala's civil war

But it is extremely rare for any top-ranking military officer to face atrocity charges arising from the 36-year civil war, which ended in 1996.

Former Colonel Juan Valencia Osorio, who was an assistant director of the presidential guard, was sentenced to 30 years in prison by the court in Guatemala City.

Two other defendants, retired General Edgar Godoy and former Colonel Juan Guillermo Oliva were cleared of ordering the murder.

'State enemy'

Prosecutors had told the court that Ms Mack had been targeted by the military, after she produced a report in 1990, blaming state-controlled anti-insurgency campaigns for killing hundreds of Mayan Indians.

The defence had argued that the presidential guard had existed solely to protect the head of state and that Mack had been no danger to the army.

"This is the lynching of military men," said defence lawyer Sergio Castro.

But prosecutor Roberto Romero told the court that Mack had known too much about the way peasants were targeted during the civil war.

"That turned her into an enemy of the state and an assassination target," he said.

UN criticism

The presidential guard has been blamed for a number of assassinations.

The BBC's correspondent in Mexico City Nick Miles says that whilst the conviction shows the willingness of judges to deal with Guatemala's past, recent reports from the United Nations mission in Guatemala, Minugua, are critical of the country's human rights record.

In recent months dozens of people working to bring former politicians to trial for their part in wartime atrocities have been intimidated.

Minugua also points out that many key parts of the 1996 peace accords have not been implemented.

Two presidents have failed to fulfil promises made in the peace accords that the presidential guard be turned into a civilian force.

The case is thought to be only the second time Guatemalan military leaders have been put on trial for wartime crimes.

In June 2001, the same court in Guatemala City sentenced three soldiers and a priest to lengthy prison terms for their roles in the assassination of Bishop Juan Gerardi.