One of Colombia's most powerful drug barons, Gilberto Rodriguez Orejuela, has been freed from prison - despite government protests against his release.

Under heavy police guard, he walked out of prison on Thursday night, after serving half of his 15 year sentence.

Cali cartel

Run by the Rodriguez Orejuela brothers Operated in the 1980s and 1990s Allegedly responsible for 80% of world's cocaine Annual profits estimated at $8bn

His release is a blow for Colombia's President Alvaro Uribe who had intervened to overturn an order given last Friday to free both Gilberto and his brother Miguel.

But a judge in the city of Tunja upheld the ruling that Gilberto should be released immediately for good behaviour.

Miguel is expected to remain behind bars after a court handed him a new four-year prison sentence for bribery earlier this week.

Together the brothers ran the notorious Cali cartel, believed to have supplied about 80% of the world's cocaine.

'Moment of pain'

The United States described the judge's decision to free Rodriguez as "unfortunate".

"The illegal activities of the Rodriguez Orejuela brothers are of concern to us and to the Government of Colombia that has made every effort to prevent their release," State Department spokesman Richard Boucher said.

Miguel Rodriguez Orejuela is to remain behind bars

Colombia's Interior Minister, Fernando Londono said he believed the immense financial power of the drug barons had corrupted the justice system, showing it was not up to the task of taking on drug-traffickers.

"This is a moment of mourning and pain for the country's image and for the administration of justice in Colombia," he said.

Correspondents say the decision could seriously affect Colombia's relationship with the US, which has heavily funded the Colombian war against drug production and trafficking.

Most wanted

Gilberto Rodriguez Orejuela, known as The Chess Player, and his younger brother Miguel controlled the Cali cartel until they were jailed in 1995.

They had been listed among the world's most wanted men.

The US Drug Enforcement Administration described their cartel - which operated in the 1980s and the beginning of the 1990s - as "the most powerful drug trafficking organisation in history".

At the time of their arrest, the Rodriguez Orejuela brothers were reported to have annual profits of $8bn.

In 1997, they were convicted and sentenced to between nine and 10 years in prison - further charges saw their sentences increased.