The US has justified its air and naval campaign as necessary to fight drug smuggling into the US.

The build-up in the Caribbean began in August with the deployment of air and naval forces, including a nuclear-powered submarine and spy planes, according to US officials.

It now includes a range of aircraft carriers, guided-missile destroyers, and amphibious assault ships capable of landing thousands of troops.

Analysis of satellite images has made it possible to identify at least six military vessels in the region over the past week.