There were a record number of large seizures of ivory in 2011 reflecting the sharp increase in illegal trade in elephant tusks, the conservation organization TRAFFIC says.

There were at least 13 seizures of caches of ivory over 800 kg each, the group said in a news release Thursday.

"A conservative estimate of the weight of ivory seized in the 13 largest seizures in 2011 puts the figure at more than 23 tonnes, a figure that probably represents some 2,500 elephants, possibly more," it said. That's up from six large seizures in 2010 with a total weight of just under 10 tonnes.

"This is the worst year ever for large ivory seizures — 2011 has truly been a horrible year for elephants," said Tom Milliken, TRAFFIC’s elephant expert, who has collected illegal ivory trade information for the Elephant Trade Information System for 23 years.

And while the number of seizures is up, most don't lead to any arrests. "I fear the criminals are winning," Milliken said.

He attributed the rise in volumes to increased demand in Asia and the increased sophistication of the criminal gangs behind the trafficking.

Most illegal shipments of African elephant ivory end up in either China or Thailand and originate in Kenyan or Tanzanian ports, TRAFFIC said.

Malaysia is frequently a transit country in the supply chain. Earlier in December,  Malaysian customs officials seized 1.4 tonnes of ivory concealed inside a shipping container en route from Kenya to Cambodia.

On Dec. 21, 727 ivory pieces were discovered inside a container in Mombasa, Kenya, and destined for Asia.

TRAFFIC is a joint program of the World Wildlife Fund and the International Union for Conservation of Nature.