Thailand's former prime minister Yingluck Shinawatra delivered a tearful closing statement to a Bangkok court on Tuesday, saying she did not act dishonestly in a multi-billion dollar rice subsidy scheme and that she was being politically persecuted.

Yingluck argued the rice scheme, which backfired costing Thailand $8 billion, benefited average Thais. The scheme appealed to agricultural voters, who make up nearly 40 percent of the labour force, and are the backbone of Yingluck's party.

"The rice policy has been proven to benefit the economy at the grass roots level and nationwide. It did not cause losses. Which is why I intended to make this rice scheme work," Yingluck told the court.

"The rice scheme was honest and correct," she added.

If convicted of negligence, Yingluck faces 10 years in jail.

Yingluck was ousted in a May 2014 coup and banned from politics for five years in 2015 but remains a figurehead of the populist movement that has won every Thai election since 2001.

The case against her is the latest twist in a chapter of political infighting that has pitted Yingluck and her brother, former prime minister Thaksin Shinawatra, against members of the Bangkok-based, military-backed establishment.

After being ousted in 2006, Thaksin fled Thailand to avoid a 2008 jail term for corruption. He has lived abroad since, but retains a strong influence over Thai politics.

A tearful Yingluck told the court she was the victim of political persecution.

"I never omitted to perform my duty ... or performed my duty dishonestly. I know that I am the victim of a deep political game," she said.

Yingluck called for justice as she arrived at the Supreme Court where more than 1,000 supporters had gathered, in defiance of a government warning not to congregate en masse and as 300 police officers stood guard. As she entered the court her supporters shouted: "Fight! Fight!".

Outside the court Ladda Boonma, 67, from Nakhon Sawan province, north of Bangkok, said she came to support the former prime minister because she had been "kind to the poor".

"I came here to show my support to Prime Minister Yingluck because she has been kind to the poor and to farmers. Why is helping farmers wrong?"

In 2011 Yingluck sailed to victory in a general election and introduced a scheme to buy rice above market prices from farmers, her core constituents, store it and resell it later at a higher price.

But the scheme backfired and caused Thailand to lose its crown as the world's largest exporter of the grain.

Thailand also ended up with 18 million tonnes of rice in stock piles which the military government has auctioned off since it took power in 2014.

Last week, the government said it had frozen assets belonging to Yingluck, including bank accounts and dozens of properties in relation to a separate, administrative order by the state to claim back money lost from the rice scheme.

A new bill passed by the National Legislative Assembly on July 13 allows Yingluck to lodge an appeal without the need to submit new evidence if she is found guilty on Aug. 25, when the court is scheduled to rule in the case.