A top US counter-narcotics official has warned that Mexico's democratic development is at stake in the country's battle against drugs cartels.

Speaking as the US Congress approved a long- awaited $400m (€253m, £200m) aid package for Mexico's anti-drug drive, David Johnson, the top counter-narcotics official at the Department of State, also gave a stark depiction of the challenges posed by the drugs industries of Afghanistan, Colombia and Burma.