Thousands of elephants are being killed in central Africa to supply an illegal ivory market in Sudan, a report says.
Africa is currently home to an estimated 400,000 to 660,000 elephants
Dr Esmond Martin, who led the research, said three-quarters of the poached ivory ends up in China - now the major market in the world for ivory.
He said he had visited 50 shops in Khartoum and Omdurman where ivory was being illegally bought and sold.
He said the trade was being openly conducted and threatened the very survival of the elephant in Africa.
Chinese oil workers
Dr Martin, who released the report on behalf of Care for the Wild International, said some 150 people were working in Khartoum, carving the ivory.
He said he counted more than 11,000 ivory pieces on sale, even though the trade was against Sudanese law.
"All the Sudanese need to do is enforce their own laws," he said.
Some 75% of the ivory is bought by Chinese customers, many of whom are working in Sudan in the oil industry.
"They are not buying small quantities, they are buying huge quantities to take back home," Dr Martin said.
According to Dr Martin, the elephants are being killed in their thousands in central Africa, principally in the Democratic Republic of Congo, the Central African Republic, Chad and southern Sudan.
To supply the market for illegal ivory in China and the Far East, it is estimated that 6-12,000 elephants are killed each year.
It is not known what percentage passes through Khartoum but Dr Martin said it was significant.