DOHA, Qatar — Proposals by Tanzania and Zambia to weaken the 21-year-old ban on ivory sales were shot down by a U.N. conservation meeting today over fears it would fuel the illegal trade of elephant tusks.

The 175-nation Convention on International Trade in Endangered Species first rejected the Tanzania proposal for a one-off sale of existing ivory stocks and then swept aside a Zambian compromise to allow for future sales of tusks.

The rulings were a rare victory for environmentalists at the two-week meeting where they have endured defeats of proposals ranging from an export ban on Atlantic bluefin tuna to a shark conservation plan to a measure to regulate trade of red and pink corals.

The proposals would have been the third and fourth such one-time ivory sales following cases in 1999 and 2008.

Prof. Samuel K. Wasser, director of the Center for Conservation Biology at the University of Washington, said there is a clear link between one-off sales and the rise in poaching. He said the sales revive dormant markets by sending consumers the message that it is OK in general to once again buy ivory and makes it difficult to differentiate between legal and illegal products.

"This is a rare victory for elephants," said Jason Bell-Leask, director of the International Fund for Animal Welfare, Southern Africa.