At the entrance to the sprawling Ivindo national park in central Gabon, wildlife guards in paramilitary uniform scour a fisherman's dug-out canoe, going through his bags of worn clothes and bait. "We're looking for arms and ammunition," one says.

Gabon, which along with Democratic Republic of Congo now has Africa's biggest forest elephant populations, is deploying scores of "eco-guards", as they are called, to ward off poachers honing in on a prime continental target.

The wild territory in the heart of central Africa's tropical forest basin on the border with Cameroon and the Congo has seen a massive jump in ivory smuggling in recent years.

About 11,000 elephants have been slaughtered for their tusks in less than 10 years in the Minkebe national park, the most threatened of three in the region, with Ivindo and Mwagna, according to the National Agency for National Parks (ANPN).

Some 100 eco-guards patrol the three sprawling parks in an increasingly dangerous job. Minkibe is the size of Belgium, with towering trees - some 150 feet high (46 metres) making aerial surveillance impossible.

Luc Machot of the non-governmental organisation Conservation Justice branded the killings as "industrial poaching".

Between "150 and 200 kilogrammes" (330 to 440 pounds) of ivory are smuggled out of the reserve every week, he says, accounting for about 15 to 20 slain elephants.

A dense terrain of some 7,000 square kilometres (2,700 square miles) with no roads or villages can only be crossed by boat and has become a lair for poachers, very hard to monitor.

Foot patrols of up to 50 eco-guards with a small military and police escort are outgunned by the poacher gangs often equipped with assault rifles. In early December, one of the guards was injured in a clash with poachers from Cameroon and had to be evacuated.

- Taking pygmies for trackers -

Getting to Minkebe is a four-day journey by boat to reach the Lele base inside the park, where Claude Angoue says that logistics are a nightmare.

After 10 years on the job, Angoue bemoans battered canoes with "broken motors", a lack of food, radio communications that are sometimes cut and the time taken for reinforcements to arrive "when there's a problem".

"Our job has become dangerous. The more arrests we make on the ground, the better armed they come. Some have hunting rifles, but we're seeing more and more Kalashnikovs," an eco-guard said.

Rostand Abaa, the chief warden of the Ivindo park, says civil warfare in the neighbouring Republic of Congo partly accounts for the "widespread circulation of military weapons" in the region.

When faced with joint patrols of Gabonese and Congolese eco-guards, smugglers resort to using pygmies -- the millennial people of the deep forests -- as trackers, with their special skills.

"Our mission is no longer simply to look out for the people who come to kill the game, it's also a matter of national security," Abaa says.

With a human population of 1.8 million, Gabon is home to more than half the forest elephants in Africa, estimated to number some 80,000. Poaching has largely depleted elephant stocks elsewhere in Africa.

Gorillas, buffalo, panthers and other large mammals also shelter in one of the last Edens on the continent.

-'Organised crime'-

President Ali Bongo Ondimba is promoting a "Green Gabon" in a bid to draw tourists, while promising tough action against smugglers.

The state prosecutor at the north eastern regional capital of Makokou, Alain-Georges Moukoko, denounces "organised crime" in the gold and ivory business and says "we need more severe punishment." At present, the maximum penalty for poaching is six months in prison.

A short jail term will never dissuade poachers while ivory fetches 80,000 CFA francs (122 euros / $133) a kilo, a notorious trader who claims to have repented, told AFP after two spells behind bars.

"The higher we go towards Cameroon, the more it's worth," says the Gabonese dealer, who wears two panther teeth on a gold chain.

Cameroon is a key transit route for ivory, which can fetch 1,000 or even 2,000 euros per kilo in China, one of the countries where it is prized. "The margin is enormous," Machot notes.

About 50 percent of the poached ivory goes to China, he says, but there are also major clients elsewhere in Asia, as well as in Europe and the United States.