Although diamond sales have soared in the last year, De Beers's profitability has not.
Ms. Gordon also said the move came when diamond sales by rebels from Angola were substantially lower.
The diamond sales have paid for a guerrilla war there.
Belgium issued new rules governing diamond sales on March 4, but the report had been largely written by then.
With an estimated $3 billion in legal diamond sales, he built Unita into a highly mobile war machine with 35,000 well-armed troops.
"The world looked the other way in Angola for most of the 1990's, while revenues from diamond sales were used to butcher innocent civilians," he said.
Last month, the council voted to ban diamond sales from the country until a certification system is put into place by the government.
"But we have had nice increases in diamond sales, especially in larger single stones," he said.
The Bush administration, however, has sought to water down international inspection and certification measures, preferring to deal with illegal diamond sales on a case-by-case basis.
"They wanted to do a proper sales agreement," he said, "and they were also looking for an advance against future diamond sales."