By Jeremy McDermott BBC correspondent in Medellin, Colombia

Colombia has seen almost four decades of violence

In a further degradation of the Colombian civil conflict, a young teacher has been murdered by left-wing rebels, after her father refused to carry out a political killing.

The woman was kidnapped and her father told she would be executed if he didn't murder a right-wing paramilitary that lived in the same town.

The father refused, and his daughter's body has just been found.

President Alvaro Uribe has condemned the killing as "madness".

Killing note

Twenty-five-year-old teacher Ana Cecilia Deque was kidnapped as she went to school on Monday.

Uribe was shocked at the "madness"

Guerrillas of the National Liberation Army (ELN) then sent her father a note.

They weren't expecting a ransom, but if he wanted to see his daughter again, he had to kill a paramilitary fighter that lived in the same town of Cocorna in the northern province of Antioquia.

He was given two days to complete the task.

He refused, and the guerrillas have executed his daughter, whose body was found with various gunshots outside the town.

'Make amends'

The news has provoked outrage in a country hardened to violence after 39 years of civil conflict.

President Alvaro Uribe appeared shocked when told the news at a conference in the Caribbean city of Cartagena, shaking his head and calling the killing madness.

Colombia's human rights ombudsman, Eduardo Cifuentes, said that the murder showed how far the guerrillas and their cause had degenerated.

"We demand the National Liberation Army make amends and that it hand the teacher's murderers over to the authorities as well as anyone else behind this act," he said.

The rebels of the ELN and the larger Revolutionary Armed Forces of Colombia (FARC) have been fighting for almost four decades to overthrow the government and install a Marxist-Leninist regime.

But they've become deeply involved in the drugs trade and kidnapping, and have less than 5% public support.

Reports from Cocorna, once an ELN stronghold, indicate that what little sympathy the rebels once had there has just evaporated.