U.S. officials, worried that a new film about the trade of "conflict diamonds" to finance African warfare might misinform the public, say international efforts to combat the illicit commerce have been successful.

Some human rights groups say, however, that illegal diamond trade still is fuelling conflict around the world.

The trade in diamonds originating in conflict zones, sometimes called "blood diamonds," has helped pay for wars in Africa that have killed millions in Angola, Sierra Leone, Liberia and Congo.

The film Blood Diamond, set amid the brutal civil war in Sierra Leone in the late 1990s, opens in U.S. theatres Friday.

U.S. State Department officials are eager to point out that the war depicted took place before establishment of an international initiative to control the trade, known as the Kimberley Process, which aims to force participants to certify the origins of the diamonds being traded.

"We feel the film provides a good historical snapshot of the diamond industry," said Paul Simons, the deputy assistant secretary of state who deals with the issue.

But the Kimberley Process fundamentally changed the rules of the game, he told reporters at a briefing aimed at trying to remove misconceptions about the current situation that the film might cause.

Simons said that in the late 1990s, experts estimated that four per cent to 15 per cent of the world's supply in rough diamonds may have originated in conflict areas. Simons believes that the Kimberley Process, which took effect in late 2002, has reduced the illicit trade to "significantly less than one per cent."

A recent report by a South African business association confirmed that figure. At the same time, the report by Business Leadership South Africa also warned that consumer concerns over "conflict diamonds pose a long-term threat to the industry."

Rights groups, including Global Witness and Amnesty International, say that even the smaller percentages of illegal diamonds need to be reduced.

"The story is clear: blood diamonds are still being sold, and consumers cannot completely trust that these blood-soaked gems are being kept out of stores," Charmian Gooch, executive director of Global Witness, said in a statement.