Ugandan authorities have seized more than a tonne of ivory, chopped into small pieces and treated with a chemical intended to prevent it being detected, the national wildlife protection service said Monday.

The haul was made in a Kampala suburb on Saturday, before it could be loaded at Entebbe international airport and flown off to an unknown destination, the authorities said.

A Liberian and two suspects from Guinea Bissau have been arrested in Kampala, Uganda's wildlife authority spokesman Simplicious Gessa told AFP.

"In a joint operation with police, we recovered over 1000 kg of ivory suspected smuggled from either Tanzania or Democratic Republic of Congo and the operation is ongoing," Gessa said.

He added that the Ugandan authorities suspect the smuggling network goes beyond the three in custody "involving shipping agents and other officials as the consignment was suspected to be going through Entebbe (airport)".

The traffickers may have used Uganda "because our laws are a little lax on trafficking", calling for harsher laws against wildlife smugglers "so that Uganda is not used as a smuggling route".

Some 30,000 African elephants are illegally killed each year for their ivory tusks, mainly to satisfy demand in the Asian market for products coveted as a traditional medicine or as status symbols.

Uganda is a key transit country for the illegal trade, especially from Congo's huge forests.

The trade is estimated to be worth $600 million annually.

According to the International Union for Conservation of Nature (IUCN), the African elephant population recorded its biggest drop in a quarter century last year, with an estimated population of 415,000 elephants, 111,000 fewer than a decade ago.