The judges' 5-4 ruling upheld a law passed by Congress in 1997 when it lifted a six-year-old ban on extradition but said it could not be applied to crimes committed before the new law took effect in December.

The court's president, Vladimiro Naranjo, conceded that the decision was likely to "do damage" to Colombia, by adding to its drug-tainted image abroad.

Straining US relations

Correspondents say the court's decision is likely to strain relations between the US and Colombia, just weeks after the inauguration of President Andres Pastrana was hailed as the start of a new era in bilateral ties.

Before his election, Mr Pastrana campaigned on a pledge to extradite any jailed drug lords wanted for trial in a foreign court.

But Mr Naranjo said the court ruling was final and not subject to appeal, and government officials immediately endorsed it despite the pressures that it might bring from Washington.

Protecting drug lords

US officials have criticised the extradition law on grounds that it protects many drug kings such as brothers Gilberto and Miguel Rodriguez Orejuela, who for years ran the Cali drugs cartel.

The brothers are serving out relatively light sentences in Bogota's La Picota prison.