Drug trafficking threatens democracy and national security both in Mexico and the United States, US anti-drugs czar Barry McCaffrey has warned.

He made the remarks in a radio interview during a visit to Mexico to examine its attempts to seal off its southern border to illegal drugs.

"Drug trafficking is a terrible external threat to democratic institutions in both countries," McCaffrey told Monitor radio.

Certification

The visit from the head of the office of the National Drugs Control Policy comes three weeks before the US government is to decide whether to certify Mexico as co-operating country in the fight against drug trafficking.

The Mexican government has launched an extensive programme to prevent Colombian cocaine from crossing its southern borders.

More than 20,000 Mexican officers are taking part in the operation, using hundreds of vehicles, boats and planes.

The estimated cost of the sea and ground initiative is $520 million.

But, even as the operation goes on, there is still considerable pressure in Washington to have Mexico decertified.

"Imperfect co-operation"

On Tuesday, just after arriving in Mexico, Mr McCaffrey said his two day visit would boost "imperfect but growing co-operation" between the two countries.

Officially, his visit to Mexico has nothing to do with the certification list.

But local analysts have little doubt that his presence in the country is linked to the process.

Mr McCaffrey will hold talks with Mexican Attorney General, Jorge Madrazo, and Foreign Minister, Rosario Green.

Operation Seal the Border

He will also travel to the south of the country to review "Operation Seal the Border."

Mexico has never failed to gain US certification since the process was implemented in 1986.

Over the past five years, Mexico has seized an annual average of more than 20 tonnes of cocaine, one tonne of marijuana and around 200 kilos of heroin.