Thailand says it has seized four tonnes of ivory hidden in bean sacks tracked from the Democratic Republic of Congo in what authorities called the biggest bust in the country's history.



The 739 elephant tusks, bound for Laos, were seized upon arrival at a port in Bangkok on Saturday after the authorities received a tip-off, the Customs Department's Director-General Somchai Sujjapongse told reporters on Tuesday.



Somchai said that the shipment, labelled as beans, was shipped out of Congo in February and went through Malaysia before reaching the Thai capital.



Al Jazeera's Scott Heidler, reporting from Bangkok, said authorities had been tracking the shipment for two months.

Somchai said authorities believe that if the ivory, worth $6m, had reached Laos, it would then have been distributed to buyers in China, Vietnam and Thailand.



Officials said the confiscated ivory would be destroyed.



Thailand is one of the top destinations for African ivory smuggling in Asia and could face international sanctions soon if it does not show progress in combating the problem.



The confiscation comes in line with beefed-up security measures to tackle ivory trafficking as part of Thailand's National Ivory Action Plan.



An amnesty for ivory owners through registration was launched in mid-February, aiming to get owners and sellers to come clean and declare their ivory. The deadline for registration is Tuesday. So far, about 150 tonnes of ivory and ivory products have been registered under this programme.



Poachers have killed tens of thousands of African elephants for their tusks in recent years to meet demand for ivory in Asia.



China has imposed a one-year ban on ivory imports amid criticism that its citizens' huge appetite for ivory threatens the existence of Africa's elephants.