The ban will go into effect after the one-off sale by four southern African nations of government-held stock of elephant tusks, thought to total about 50 tonnes, according to non-government organisations who monitored the negotiations.

The agreement, which comes after weeks of sometimes fierce debate at the 171-nation Convention on International Trade in Endangered Species, was formally submitted by Chad and Zambia "on behalf of Africa."

"This African solution to an African problem marks a great step forward for wildlife conservation," said CITES secretary general Willem Wijnstekers.

"It is good news for the elephants and the people who live alongside them," he said.

At stake is the future of the world's largest land mammal, which once numbered several million.

A century of hunting and poaching -- which has increased sharply in the last six years -- has reduced the African elephant population to approximately 500,000.

Experts estimate that some 20,000 elephants are illegally killed every year.

The one-off sale would cover ivory stocks in Botswana, Namibia, South Africa and Zimbabwe registered as of January 31, Nithart said.

These south African nations opposed a moratorium, and had earlier called annual trade quotas and stock sales of up to 140 tonnes.

The sale will go to Japan, the only country authorized by CITES to purchase ivory.