BANGKOK (Reuters) - A rice-subsidy scheme introduced by Thailand's ousted former Prime Minister Yingluck Shinawatra lost 518 billion baht (S$20.38 billion), the Finance Ministry said on Thursday.

The scheme, which paid farmers above-market rates for their crop, helped bring Yingluck to power in a landslide election in 2011 due to support from farmers mostly in the country's north and northeast.

However, the scheme backfired when the government failed to sell rice to pay arrears to angry farmers, leaving Thailand with massive stockpiles. The stockpiles are now estimated at 19.2 million tonnes, said Rangsan Sriworasart, permanent secretary for the Ministry of Finance.

Yingluck was forced to step down in May when a court found her guilty of abusing power in the transfer of an official. Days later, the military staged a coup following six months of street protests aimed at ousting Yingluck.

The military put a halt to state rice sales and General Prayuth Chan-ocha, the coup leader and current Prime Minister, has ruled out a new rice price intervention scheme.

In its record year for exports in 2011, Thailand shipped 10.6 million tonnes of rice.

The latest audit found that around 70 percent of the rice held in stockpiles is deteriorating.

Rangsun said an official audit of state stockpiles would be announced at a later date by the prime minister's office.