The world must clamp down on the illegal global wildlife trade, the head of the United Nations environment agency warned on Sunday, calling it a multibillion-dollar criminal business that is threatening to wipe out some of the planet's most iconic species.

Achim Steiner, executive director of the United Nations Environment Program, made the call during the opening meeting of the 178-nation Convention on International Trade in Endangered Species, or CITES, in Bangkok. He cited the massive upsurge in poaching of Africa's endangered elephants and rhinos, whose slaughter - the worst in two decades - is being driven by rising demand in Asia for their tusks and horns.

"The backdrop against which this meeting takes place should be a very serious wake-up call for all of us," Steiner told some 2,000 delegates assembled at a convention center in the Thai capital.

Wildlife trafficking "in a terrible way has become a trade and a business of enormous proportions - a billion-dollar trade in wildlife species that is analogous to that of the trade in drugs and arms," Steiner said. "This is not a small matter. It is driven by a conglomerate of crime syndicates across borders."

Slowing the slaughter of African elephants and curbing the trade in "blood ivory" will be at the top of the agenda during the global biodiversity conference, which lasts two weeks. Around 70 proposals are under consideration, most of which will decide whether member nations increase or lower the level of protection on various species. These include polar bears, rays and sharks that are heavily fished for shark fin soup.

There are proposals, too, to regulate 200 commercially valuable timber species - half from Madagascar - and ban their trade unless it can be shown they were harvested legally.

Steiner said up to 90 percent of the world's timber trade is illegal, a business worth at least $30 billion per year.

Prior to the establishment of CITES in 1973, there was no international regulation of the cross-border trade in wildlife. Most of the agreements regulating the 35,000 animals under CITES' purview aim not to outlaw trade, but to ensure it remains sustainable.

One of the convention's success stories since then has been the African rhino, which numbered just 2,000 four decades ago. The population swelled to 25,000, but over the last five years poaching has skyrocketed again. Last year, 668 rhinos were killed in South Africa alone. As with the elephant crisis, the culprit is largely demand from Asia, where their horns are highly desired because they are believed to have medicinal properties.

CITES Director-General John Scanlon said the slaughter of African elephants and rhinos was at its worst in decades, a level that "could threaten the survival of the species themselves". He blamed poachers, rebel militias and mafia-like crime syndicates that smuggle animal parts across borders.

"This criminal activity poses a serious threat to the stability and economies of these countries. It also robs these countries of their natural heritage, their culture heritage, and it undermines good governance and the rule of law," Scanlon said.

"These criminals must be stopped, and we need to prepare to deploy the sorts of techniques that are used to combat the trade in narcotics to do so.

"We know the way. We now need the collective will," Scanlon said. "Right here, right now in Bangkok is when we must come together to turn the tables on serious wildlife crime."