The UN's wildlife trade organisation has turned down Tanzania's and Zambia's requests to sell ivory, amid concern about elephant poaching.
The countries asked the Convention on International Trade in Endangered Species (CITES) meeting to permit one-off sales from government stockpiles.
The ivory trade was banned in 1989, but two sales have since been granted to nations showing effective conservation.
Kenya withdrew a bid to ban sales for 20 years, after finding little support.
Most conservation groups were delighted that the Tanzanian and Zambian bids were turned down.
"This is a real victory for elephants," said Jason Bell-Leask, director of Southern African operations with the International Fund for Animal Welfare (Ifaw).
Others argued that the real issue facing African elephants was poaching, not the occasional legal sale.
"While the issue of whether sales should be allowed to proceed or not has dominated much of the discussions here... the key driving force behind the ongoing elephant poaching is the continued existence of illegal domestic ivory markets across parts of Africa and Asia," said Steven Broad, executive director of Traffic, the body charged with monitoring the illegal wildlife trade.
Traffic's latest report shows that poaching and smuggling are rife in West Africa in particular, with several Asian nations complicit in smuggling.
Nigeria, the Democratic Republic of Congo and Thailand are picked out as the worst offenders.
Organised crime syndicates are increasingly involved in the lucrative trade.
"Poaching and illegal ivory markets in central and western Africa must be effectively suppressed before any further ivory sales take place," said Elisabeth McLellan, species programme manager with WWF International.
An expert report released on the eve of the CITES conference raised concerns about the extent to which organised crime rings are involved in Tanzania's poaching and smuggling operations.
Although commending the national wildlife services for their "professional" approach, it noted signs of a declining commitment to law enforcement and a lack of co-ordination between wildlife and customs services.
Traffic also noted that almost half of the ivory in the government's stockpiles - which would have been the source for the ivory sales - was of unknown origin.
As a result of this, it recommended rejecting Tanzania's bid. Similar misgivings also led to a recommendation to reject the Zambian proposal.
Both countries also failed in bids to switch their elephants from CITES Appendix One to Appendix Two, which would have permitted trades under certain restrictions.
The vote on the Zambian proposal was extremely close, and Zambia may seek to re-open the issue on Thursday, the conference's final day.
A number of conservation and animal welfare groups say the one-off ivory sales ensure there is an ongoing market into which crime rings can sell poached ivory, although the data is hard to interpret.
However, Eugene Lapointe, president of the IWMC World Conservation Trust and a former CITES secretary-general, said the one-off sales generated revenue that under CITES rules had to be ploughed back into elephant conservation.
"The situation is simple: prohibition plus poverty causes poaching," he said.
"Where people are given incentives to conserve, elephant stocks increase and poachers are put out of business."
The last legal sale - in Botswana, Namibia, South Africa and Zimbabwe - took place in 2008.
Over the weekend, the CITES meeting in Doha, Qatar also turned down a bid to ban trade in red and pink corals from the Mediterranean Sea.
Conservation groups say the corals - which are used in jewellery - are threatened with local extinction if extraction continues.