A U.N. environmental agency on Thursday postponed a plan to allow three southern African states to make a one-off sale of 60 tonnes of elephant ivory.
The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) said in a statement that more information was needed on African elephant populations and on rates of poaching.
Ivory sales have been banned internationally since 1989. But four years ago CITES agreed in principle to the sale of 20 tonnes by Botswana, 10 tonnes by Namibia and 30 tonnes by South Africa to help them cut burgeoning stockpiles.
The ivory intended for sale was to come from elephants that died of natural causes or were legally culled.
The sales were made conditional on a system being in place to monitor possible illegal killing of elephants and to track illegal sales in the main market, Japan.
"The CITES standing committee determined that this condition has not yet been satisfied, and the sales may not go forward," the U.N. agency said in a statement.
The issue will be reviewed at the next meeting of the standing committee in May 2007.
Opponents welcomed the move, but said that postponing a decision sent a mixed message.
"Uncontrolled illegal ivory trade and elephant poaching persist in both Africa and Asia," said Ronald Orenstein of Humane Society International.
"By keeping the door open to further sales ... the committee risks alerting poachers that they can step up their efforts," he added.
But supporters of the sale say offering a legal market could help prevent poaching, for which there are no reliable figures.