The International Criminal Court is to investigate companies suspected of dealing in so-called "blood diamonds" - gems sold to finance civil wars in Africa - originating in the Democratic Republic of Congo.
Campaigners say diamond sales in Africa have funded civil wars
The mass killings in the DR Congo was the "most important case since World War Two", chief prosecutor Luis Moreno Ocampo warned on Tuesday, adding that exposing international money flows will be an important part of his work.
The ICC which came into existence last year and has the mandate of trying war crimes and genocide will investigate businesses in at least 29 countries.
More than three million people died during DR Congo's five year war which pulled in neighbouring countries and ended in 2002.
Since 1999 at least 50,000 people have died in cashes in Ituri where rival groups have fought for control of natural resources, including diamonds and coltan which is used in mobile telephones.
"If we are not stopping the money flow, killing will not stop in
Ituri (the war-torn region in northeast DR Congo)," the chief prosecutor said.
Business 'war criminals'
Foreigners who had bought blood diamonds from the country could be charged with complicity in war crimes and genocide, he added.
Information would be collected from national prosecutors in countries as far away as Canada and the United States where the links to the purchase of blood diamonds have been discovered, he said.
Moreno-Ocampo says 29 businesses will be investigated
"If they received diamonds and knew that the people
delivering them were getting them because of genocide then they could well be part of the crime," he said.
"Follow the trail of the money and you will find the
criminals. If you stop the money then you stop the crime."
The investigations will begin in the autumn.