Various wildlife conservation groups share these concerns.
The CITES decision is "a disgrace," said Peter Pueschel of the International Fund for Animal Welfare (IFAW), based in Yarmouth Port, Massachusetts.
"Japan clearly fails to meet the bar set by the CITES framework for such sales," he added in a statement.
Pueschel noted that 2.8 tons of illegal ivory was seized in Osaka, Japan, only last year (see a photo of the ivory seizure).
The price of ivory in Japan has risen to a record of U.S. $850 per kilogram (2.2 pounds), from U.S. $500 per kilogram in 1994.
IFAW says demand for ivory is driving the slaughter of at least 20,000 elephants a year.
A recent study also suggested that Asian criminal gangs are behind an upsurge in trade in illegal ivory.
TRAFFIC, a wildlife trade-monitoring network run by the conservation nonprofit WWF and the United Nations' World Conservation Union, found that seizures of contraband ivory weighing at least a ton have almost doubled in recent years.
The study blamed these increases on traffickers from China and other Asian countries.
Yet WWF supports the newly approved ivory sale to Japan, which follows a similar agreement made in 1997.
There is no evidence that illegal trade in ivory is fueled by a one-off sale, according to Joanna Benn of the WWF Global Species Programme.
"This is probably going to be the most monitored controlled sale in the history of conservation," Benn said.
"All the revenue from the stockpile has been pledged to go straight back to elephants and conservation," she added.
Recent research shows that West and Central Africa are the main sources of illegal ivory, WWF says (Africa map).
Namibia, Botswana, and South Africa, meanwhile, "have the strongest elephant management regimes anywhere in the world at the moment," Benn said. "This is why they've been so successful with their elephant populations."
In recognition of this, CITES allows southern African countries to deal in certain elephant products through a permit system.
The current 12-day conference will also debate proposals to grant export quotas to Botswana, South Africa, Namibia, and Zimbabwe for elephant hides, leather goods, and live animals.
Delegates will also vote on whether to relax ivory trade restrictions, which in the future could lead to limited sales.
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