More than two decades after the collapse of the Soviet Union, the planet's largest stockpile of nuclear weapons materials remains insecure, according to a series of US intelligence reports obtained by Al Jazeera's Investigative Unit.
In the wake of the Soviet collapse into 15 independent states, hundreds and perhaps thousands of grammes of nuclear material - including highly enriched uranium used in atomic bombs - were spirited away from Russia's nuclear heartland.
"We assess that undetected smuggling of weapons-usable nuclear material has occurred, but we do not know the total amount of material that has been diverted or stolen since the dissolution of the Soviet Union,'' the US Director of National Intelligence (DNI) said in a 2011 report, the latest unclassified document released by the intelligence community.
"We judge it highly unlikely that Russian authorities have been able to recover all of the stolen material."