A conservation group claims Chinese officials used a state visit by President Xi Jinping to smuggle ivory out of Tanzania.
The London-based Environmental Investigation Agency report said thousands of kilograms of ivory hidden in diplomatic bags were flown out of Tanzania on Mr Xi's plane, the BBC reported.
The EIA said Tanzania was the largest source of poached ivory in the world.
China has dismissed the allegations and a Tanzanian government spokesperson, Assah Mwambene, dismissed the group's findings.
"It's very unfortunate that a very credible institution like the agency can produce a very questionable report, to the effect of mentioning a person to a level of a head of state - that his private jet, his presidential jet, was able to carry pieces of ivory from Dar es Salaam. I mean, this is stupid nonsense."
The ivory trade was banned in 1989 by the Convention on International Trade in Endangered Species of Wild Fauna and Flora. Both China and Tanzania are signatories.
China does have about 150 legal government-licensed ivory shops, which sell ivory collected before the ban and are the only places allowed to sell ivory to individual buyers.
Earlier this year China for the first time destroyed a large quantity of confiscated ivory, in a public event described by conservation groups as a landmark move.
Just over six tonnes of carvings, ornaments and tusks amassed over the years were fed into crushing machines.