Mexican drug cartels whose operatives once rarely ventured beyond the US border are dispatching some of their most trusted agents to live and work deep inside the US — an emboldened presence that experts believe is meant to tighten their grip on the world’s most lucrative narcotics market and maximise profits.

A drug kingpin in Mexico is being named as Chicago’s public enemy No 1 — a label first given to gangster Al Capone and one that hasn’t been used since the 1930s.