A Thai policeman has been arrested after he was caught trying to smuggle 20 elephant tusks, officials said Sunday.

The haul was discovered when the suspect -- in plain clothes but driving a police van -- was stopped at a checkpoint in the southern province of Chumphon on Saturday, Police Colonel Chalard Polnakarn told AFP.

"We found 10 pairs of elephant tusks in the van and charged him with illegal possession of elephant tusks, which he confessed to during the investigation," Chalard said.

The origin of the tusks was unclear.

International trade in elephant ivory, with rare exceptions, has been outlawed since 1989.

But a rise in the illegal trade in ivory has been fuelled by demand in Asia and the Middle East, where elephant tusks are used in traditional medicines and to make ornaments.

Conservationists say ivory from Africa is often smuggled into Thailand and passed off as coming from Thai elephants, as a legal loophole allows the legal trade in ivory from domesticated elephants.

Wildlife campaign group Freeland praised the latest seizure as a "valiant act of fighting corruption to protect wildlife".

"We need more officers like them to fight this new form of transnational organised crime," Freeland director Steven Galster said in a statement.

Freeland said that in the past year thousands of tusks had been seized as they were smuggled into Asia from Africa due to "rampant elephant poaching".

It comes as Thailand prepares to host the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES) in Bangkok in March.