Thieves stole three tonnes of ivory tusks from a strong room at the Zambia Wildlife Authority (ZAWA), the biggest heist of its kind in the country, an official said Wednesday.

Two game scouts were arrested over the theft of the elephant tusks valued at 2 billion kwacha ($383,658), which the authorities believe occured last week at the ZAWA headquarters in Chilanga, near the capital Lusaka.

"During the routine checks in the strong-room ZAWA officers discovered that three tonnes of ivory valued at 2 billion kwacha have gone missing," ZAWA director general Edwin Matokwani told AFP.

"So far two game scouts have been arrested in connection with the theft," he said.

ZAWA is tasked with wildlife conservation and curbing poaching which is on the rise in the southern African country.

Two years ago Zambia and Tanzania failed to convince a UN Convention on the International Trade of Endangered Species of Fauna and Flora (CITES) to allow them to hold one-off sales of their ivory stockpiles.