JOHANNESBURG-Thousands of conservationists and top government officials went into talks in Johannesburg Saturday to thrash out international trade regulations on elephant ivory, rhino horn and hundreds of endangered wild animals and plants.

The booming illegal trade of wildlife has put huge pressure on a treaty signed by more than 180 countries - the Convention on International Trade in Endangered Species (CITES). The plight of Africa's rhino and elephants, targeted for their horns and tusks, is expected to dominate much of the 12-day meeting.

"We are now embarking on the largest meeting ever in the 43-year history of CITES," the convention's secretary general John Scanlon said at the start of the talks.

"We are going to review trade controls of close to 500 species of wild animals and plants. High on the agenda we have the African elephants, the rhino, the pangolin... the silky shark," he said.

Illegal trade in wildlife is valued at around $20 billion (18 billion euros) a year, according to CITES.

The meeting will consider whether to tighten, ease or not impose trade controls on the myriad of species, including special types of wood.

Scanlon lauded the high level of political support being shown for tackling the illicit wildlife trade, which is ranked among the world's largest illegal businesses alongside arms, counterfeit goods, drugs and human trafficking.

South Africa's President Jacob Zuma opened the Johannesburg talks.

"Levels of exploitation of some animal and plant species are high and the trade is capable of heavily depleting their populations and even bringing some species close to extinction," said Zuma.

The United Nations Environment Programme (UNEP) chief Erik Solheim called for more action to protect wildlife.

"We are not doing as well when it comes to protecting species. There is huge challenges and that is why this conference is so important. We need to step up to protect the elephants, the rhinos, the orangutans," said Solheim.

Scanlon said while all 183 CITES parties are "deeply committed to the survival of wild animals and plants, they sometimes have differing views on the best way to achieve this."

A coalition of 29 African countries is pressing for a total halt to the ivory trade to curb poaching of elephants, but other delegates believe it would only fuel illegal trading.

A recent census revealed that the savannah elephant population has declined by 30 percent over seven years.

Britain's Prince William said in a pre-CITES speech this week that the census confirmed that "one of our planet's most treasured species is on course for extinction at the hands of poachers and traffickers".

He added that when he was born there were one million elephants roaming Africa, but they could be extinct in the wild when his one-year-old daughter Charlotte turns 25.

CITES forbids trade in elephant ivory, but Namibia and Zimbabwe have made a proposal asking for permission to sell off stockpiles to raise funds for local communities that co-exist with the animals.

On rhino horn trafficking, CITES banned that trade 40 years ago, but prohibition has not reduced illicit hunting, which has recently boomed in South Africa.

Around 5,000 white rhino - a quarter of the population - have been slaughtered over the past eight years, with the majority killed in South Africa, home to 80 percent of the world's rhino.

Rhino poaching is driven by insatiable demand in Vietnam and China for the horn, which is mistakenly believed to have medicinal powers curing everything from hangovers to cancer.

Other species high on the CITES radar are devils ray, rock geckos, tomato frogs and the African grey parrot.

Scanlon warned that illegal wildlife trafficking was "occurring on an industrial scale, driven by transnational organised criminal groups".

Besides animals, timber will be a focus.

When it first came into force in 1975, CITES only regulated a handful of timber species, but three years ago there were 600 types of timber listed under its appendices.

This year there are 250 species proposed for listing, especially of sought-after rosewood.