"The best way is to make public details of the agreement for the sake of cooperation and bilateral relations," Surin said.

More transparency on the agreement signed in 2004 was needed to prevent any misunderstanding or impact on Thai feelings towards Australia, he said.

"It's not appropriate to secretly transfer the elephants. I regard this as an attempt to steal national property and it affected the dignity of the country and people as a whole," he said.

"I wonder why the government promised at the beginning that it would have DNA tests on the elephants. But then they turned around and said the DNA test would be too complicated," said Surin, who is a deputy Democrat Party leader.

Activists had demanded the tests to confirm if the jumbos were born in the wild or in captivity.

"Now the government is allowing the secret transfer of the elephants. This signalled that there is something hidden on the matter,"  Surin added.

The eight elephants were heading to Australia in exchange for koala bears and other animals. Protests both here and in Australia had delayed the transfer for more than 1½ years. Thai non-government organisations had blocked the transfer of the elephants from Kan-chanaburi but a renewed attempt was successful on Sunday after the elephants were transported secretly to U-Tapao Airport during the night. Police and soldiers set up checkpoints to block the protesters.

The elephants are now settling in for three months of quarantine in the Cocos Islands, officials said.

A last-minute bungle on Sunday meant the group was split up because the Russian transport plane flying them to the Indian Ocean territory was smaller than ordered.