An international anti-corruption watchdog says Afghanistan's war is being fueled by the country's mining sector, with armed groups — including the Taliban — earning $20 million from illegal mining of lapis lazuli.

A report by Global Witness released on Monday says that lapis lazuli, a blue stone almost unique to Afghanistan, should be classified as a "conflict mineral."

It says the northern Badakhshan province where lapis lazuli is concentrated has been "deeply destabilized" by violent competition for control of the mines between local strongmen, law makers and the Taliban.

Badakhshan is a microcosm of what is happening across Afghanistan, with mining being the Taliban's second biggest source of income, after drugs.

The Taliban insurgency is in its 15th year.

Afghanistan's mineral assets are believed to be worth billions of dollars.