Mexico's former anti-drugs czar has been sentenced to 40 years in prison for drug trafficking and involvement in organised crime.

Prosecutors said General Jesus Gutierrez Rebollo, who headed the now defunct National Institute to Combat Drugs, helped Mexico's leading drug traffickers export cocaine to the United States.

The sentence came at the end of a long legal process during which several key witnesses died or disappeared.

The 65-year-old retired officer has always maintained that he was innocent.

He had been convicted in 1997 of other drug crimes and sentenced to more than 31 years in prison, a term he is currently serving.

Authorities said General Gutierrez had links to a notorious drug trafficker, the late Amado Carrillo Fuentes.

Fuentes was known as the "Lord of the Skies" for flying planes filled with cocaine.

'Exemplary path'

In 1996 General Gutierrez became the first member of the military to head the nation's war on drugs.

At one point he was lauded for his "exemplary" path by US anti-drug czar Barry McCaffrey.

Correspondents say General Gutierrez is one of the most senior officials yet convicted of drugs-related corruption in Mexico.

Among 10 witnesses who mysteriously died or vanished since the general's arrest was his former aide Jorge Humberto Capelleti Gonzalez.

He was fatally shot in an apparent robbery, but authorities at the time did not rule out the possibility that he had been in revenge.