Endangered animals are being killed in "horrifying numbers" and efforts to tackle the crisis must be accelerated, the Duke of Cambridge has said.
Speaking at an international conference in Vietnam, Prince William said there was "much to be proud of" when it came to efforts to halt illegal poaching.
But he said the "brutality" of poachers and crime gangs was still escalating.
He called on the UK to pass a total ban on the domestic ivory trade, as has been done by China and the US.
While the international trade in ivory has been banned since 1989, it is still possible to sell antique ivory in the UK as long as it was carved before 1947.
The duke urged the UK government to push ahead with a total ban on the trade, in a bid to protect elephants.
"China has already signalled a total ban, the USA has instituted one, and other nations, including the United Kingdom, are considering it," he told the conference on illegal wildlife trade in Hanoi.
"We know now what previous generations did not - ivory treated as a commodity is the fuel of extinction.
"Ivory is not something to be desired and when removed from an elephant it is not beautiful.
"So, the question is: why are we still trading it? We need governments to send a clear signal that trading in ivory is abhorrent."
A Department for Environment, Food and Rural Affairs spokeswoman said the UK was doing "more than ever before" to tackle the illegal wildlife trade.
Prince William is on a two-day official visit to Vietnam to highlight the damage the illegal trade in wildlife has on some of the world's most iconic animals.
"We know that we aren't moving fast enough to keep up with the crisis. Rhinos, elephants, pangolins, lions, they are still being killed in horrifying numbers," he told the conference.
"While we've made progress, the truth is we are still falling behind. A betting man would still bet on extinction."
He said the "organised crime syndicates we are up against are much more agile than we are".
"We are getting cleverer, but we need to admit that they are getting much cleverer as well," the duke added.
"Their brutality continues to escalate, with many more rangers killed since we gathered in London two years ago."
In 2014, the UK hosted a summit in London to bring leaders and key figures together from around the world to focus on tackling the issue.
It resulted in the signing of the so-called London Declaration, strengthening a commitments to stop the illegal wildlife trade.