Prince Charles, his son Prince William and the British government were hosting the international conference aimed at improving law enforcement in the mainly African countries where poaching is rife, and at stemming growing demand in Asia.
Opening the London Summit on Illegal Wildlife Trade, Charles said that while it was important to tackle poachers, the key thing was to "attack demand" for rare creatures to produce traditional medicines and other products.
"Most recently, demand from Asia - particularly China - has fuelled the trade, but we also know that the United States and Europe are contributing to it," said Charles.
Crucially, China's Forestry Vice Minister Zhang Jianlong will be at the summit, along with four African heads of state, from Chad, Gabon, Botswana and Tanzania.
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Vietnam, a big market for rhino horns, is also attending.
British Foreign Secretary William Hague said endangered species faced an "unprecedented crisis".
He said the illegal wildlife trade was a "global criminal industry, ranked alongside drugs, arms and people trafficking" and that terrorist groups were benefiting from the trade.
"We want to support the amazing work already done in Africa, Asia and elsewhere and send the unequivocal message that this stops now. We will confront the crisis and we will beat it," he said.
Around 25,000 elephants are killed each year by poachers, according to official estimates, and South Africa lost around 1,000 rhinos last year compared with just 13 in 2007. Central African countries fare worst, with Gabon experiencing the biggest losses.
Prince William made an impassioned plea at an evening reception last night for the "despicable" illegal trade to be stamped out.
"Tonight we are here with a single, shared purpose -- to use our collective influence to put a stop to the illegal killing and trafficking of some of our world's most iconic and endangered species," he told guests.
Charles has long been a champion of environmental issues.
His eldest son is following in his footsteps -- he quit the British military last year to head up a new global conservation group called United for Wildlife.