Global Witness says companies - including Apple, Tesla and Intel - are relying on the due diligence scheme to source minerals that are widely used in electronic equipment such as mobile phones, computers and automotive and aeronautical systems.

Those behind the initiative have denied the allegations.

For years there have been warnings that some minerals sourced in DR Congo that are used in electronic devices are from mines controlled by armed groups.

A scheme was launched to try to prevent these so-called "blood minerals" reaching the international market.

But Global Witness says it has uncovered compelling evidence that the International Tin Supply Chain Initiative (ITSCI) is failing.

It says the scheme is being used to launder tin, tantalum and tungsten from mines controlled by militia or where children work.

Global Witness says companies like Apple, Tesla and Intel need to do more to ensure their minerals are not fuelling conflict.