Thailand is sitting on around 17 million tonnes of the grain, accumulated under a subsidy scheme run by ousted Prime Minister Yingluck Shinawatra, whose government paid farmers well above market rates for their crops.
Government officials had indicated around 900,000 tonnes had been sold in the tender launched on Jan. 29 but Commerce Minister Chatchai Sarikulya said on Monday that some companies did not meet requirements and had been disqualified.
The Commerce Ministry expects to hold another tender for around 1 million tonnes towards the end of February.
Around 850,000 tonnes of 5 percent broken rice and around 150,000 tonnes of jasmine rice were initially offered in January.
An official from the commerce ministry said 496,243 tonnes of rice was sold in all, for 7.85 billion baht ($241 million). He gave no breakdown but the total gives an average price per tonne of around $485.
The common 5 percent broken white grade was offered at $413 per tonne on Monday.
The original sale was equivalent to nearly 10 percent of Thailand's annual rice exports and the prospect of increased shipments from the world's largest rice exporter has helped push Vietnam's benchmark price to a 15-month low.
The authorities have held four, smaller tenders since the military seized power last May. Including its latest tender, they have now sold 1,177,983 tonnes for around 17.21 billion baht ($528 million), the Commerce Ministry said.
Yingluck was removed from office just days before the coup in May. The rice scheme was hugely popular among the rural electorate, which remains loyal to her, but it was reviled by her opponents, who called it expensive and corrupt.
Yingluck was found guilty of negligence over the scheme in January and banned from politics for five years.
According to some estimates, the scheme may eventually cost the state around $15 billion as the prices won in tenders have been well below the price the government paid farmers. Only 10 percent of the stockpiled grain is now of standard export quality.
Thailand exported around 10.8 million tonnes of rice in 2014, a record high, according to the Commerce Ministry, topping its previous record of 10.4 million tonnes in 2011. Shipments plummeted when the subsidy scheme forced up prices but the state tenders could help exports set another record high this year.