details are emerging of links between al-Qaeda and the illicit trade in so-called "blood diamonds" bought from rebel groups in Africa.
The vast sums of money and weapons exchanged in return for the gems have helped fuel some of the bloodiest civil wars in Africa.
Campaigners say diamond sales in Africa have funded civil war
At the time of the 1998 bombings of the United States embassies in Kenya and Tanzania, al-Qaeda allegedly transferred cash into high-value commodities, including diamonds.
Several members of al-Qaeda's inner circle bought gems in Liberia and from Revolutionary United Front (RUF) rebels in Sierra Leone, according to research first published by the Washington Post
The move into diamonds came as al-Qaeda's assets were frozen.
Much of the evidence comes from Western intelligence reports and from the trials of al-Qaeda suspects after the 11 September attacks and the bombings of US embassies in East Africa.
"Diamonds are an extremely highly concentrated form of wealth and they retain their value," said Alex Yearsley from the campaign group Global Witness.
Al-Qaeda also bought diamonds as well as gemstones in Tanzania, he said.
Global Witness has estimated that al-Qaeda laundered $20m through purchasing diamonds.
Our goal is to sever links between conflicts and the legitimate diamond trade
Mark Van Bockstael, Diamond High Council
Facing financial difficulties in 1993 following the establishment of operations in Sudan, the organisation is said to have bought and sold gems to raise funds.
Many of the diamonds were mined by the RUF rebels, whose trademark during Sierra Leone's civil war was to hack off the hands of their victims.
Payment for the diamonds - which are the subject of United Nations sanctions designed to prevent their trade from fuelling civil war - was made in cash or weapons.
Other groups have used African "conflict diamonds" to fund their operations.
"Hezbollah (a Shiite Muslim organisation linked to Lebanese activists) fundraised through diamonds. They used the Lebanese diaspora in Western and Central Africa. Israel tried to shut down networks in Sierra Leone," said Mr Yearsley.
"[Liberia's President] Charles Taylor used a lot of diamonds to create a lot of mayhem."
In January 52 countries implemented the Kimberley Process Certification Scheme for trade in rough diamonds which means they will only accept gem imports which are certified not to have come from rebel-held areas.
The uncut gems have to be transported in tamper-proof containers.
The Kimberley scheme covers trade in rough diamonds
Fearing an anti-diamond campaign similar to the anti-fur lobby which wrecked the fur industry, most diamond buyers are co-operating with the move.
"Our goal is to sever links between conflicts and the legitimate diamond trade," says Mark Van Bockstael of the Diamond High Council in Antwerp.
But according to Clive Wright, head of Britain's diamond office, the Kimberley Process lacks the ability to monitor itself.
"Governments are yet to swallow hard and say: 'Yes, we will check up on each other'."
There are other problems. Several countries do not raise enough tax from diamond exports to make implementing the scheme worthwhile.
Certificates for each diamond cost about $3.
In some cases, the implementation of the Kimberley Process will lead to short term decreases in tax revenue from the gems.
The export of diamonds from Africa in their rough form also discourages the establishment of gem polishing industries which could provide employment for local people.
Diamond dealers also say the legislation can do little to prevent conflict diamonds from reaching Europe given the continent's vast unmanned borders.
"Some companies are honest but other companies want to buy diamonds and where they come from is of little or no concern," said Christine Gordon, a diamond expert who was part of a United Nations monitoring programme in Angola.
But although the Kimberley Process may have shortcomings there is hope that it will help give the diamond industry a clean bill of health.
Around 4% of gems on the world market are classed as "conflict diamonds".
"We can make an impact on conflict diamonds... and prevent the dreadful scenes we saw in Sierra Leone. We need to protect a legitimate industry which employs huge numbers of people," added Mr Wright.