Colombia's highest court has also asked Colombian prosecutors to determine whether or not presidential aides conspired to undermine any investigation.

Justice Francisco Ricaurte asked Alvaro Uribe, the president, to explain why aides met Antonio Lopez, a former paramilitary who acted as a spokesman for former fighters and with a lawyer who has represented paramilitaries.

The meeting is alleged to have taken place at the presidential palace earlier in the year. Uribe denies any wrongdoing.

Lopez was shot dead by unidentified men in July in Medellin, a city in the northeast of the country.

About 60 politicians are suspected of having links to the country's various paramilitary groups, including 32 current or former members of congress. The congressmen are now behind bars.

Thirteen members of the United Self-Defence Forces of Colombia (AUC) have been extradited to the US and a further 32,000 members of the militia have laid down their weapons after a deal with the government to limit prison terms.