Mexico's drug cartels are carving out new territory in Central America, in some of the poorest and most fragile countries in the hemisphere.

In an interview with Al Jazeera's Lucia Newman, President Alvaro Colom said international drug trafficking gangs are the biggest threat facing Guatemala and the region.

"Fundamentally I think we made a mistake, a miscalculation, of the scale of the problem that existed within our security forces," Colom said.

"We are witnessing a very serious aggression, which is part of a regional phenomenon, we are co-ordinating responses [to drug trafficking] with Mexico but the aggression is very strong."

The cartels, with their tens of billions of dollars in revenue each year, use airplanes and even submarines to move cocaine from Colombia into the region. Under attack in Mexico, the Zetas, a drug gang formed by former Mexican special forces soldiers, have built their own airstrips in the Guatemalan jungle.

Colom said some parts of his country near the Mexican border are currently controlled by the cartels. The government is fighting back.