Colombian President Alvaro Uribe has halted the release from prison of two of the country's most notorious drug traffickers, Gilberto and Miguel Rodriguez Orejuela.

The government has prohibited the release... as long as there remain judicial doubts

President Uribe

Mr Uribe said the government had blocked their release - ordered by a judge earlier this week - while the legitimacy of the ruling was investigated.

In a move that took the hardline president by surprise, a magistrate ruled that the men - who controlled the powerful Cali cocaine cartel - were eligible for release after serving three-fifths of their sentence with good behaviour.

As well as a high-level inquiry into the matter, Mr Uribe has demanded that Judge Pedro Jose Suarez be investigated.

I'm convinced these men, with their gigantic economic power, are producing a judicial result not according to evidence

Fernando Londono, Interior Minister

The head of the prison where the brothers are being held has already been suspended after recommending their release.

Interior Minister, Fernando Londono, said he believed the immense financial power of the drug barons had corrupted the justice system and that this showed it was not up to the task of taking on drugs traffickers.

US relations

Local radio reported that four luxury cars were parked outside the jail on Friday, waiting for the release of the Rodriguez Orejuela brothers.

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

But hours after the country's prosecutor general confirmed he had been informed of the controversial ruling, the government vowed to fight it.

"We're going to try to block this ruling. We think it's impossible it can be legal because they have not served their sentence," Attorney General Luis Camilo Osorio said.

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

Judicial experts consulted by the El Tiempo newspaper said a new extradition request by the United States could prevent the men from walking free.

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.

President Uribe's government is studying the legality of the ruling

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 be responsible for 80% of the world's cocaine and their annual profits were estimated at $8bn.

In 1997, they were convicted and sentenced to between nine and 10 years in prison - further charges saw their sentences increase to more than 20 years.

They have spent time in several Colombian prisons and were moved last month to a prison in Bocaya, about 120 kilometres north-east of the capital, Bogota.