BANGKOK (AFP) - More than 4,000 police will guard Thailand's Supreme Court on Friday (Aug 25) when judges announce a verdict in the case of ousted prime minister Yingluck Shinawatra, accused of negligence over a costly rice subsidy policy.

Thailand's first female prime minister, toppled by a military coup in 2014, faces up to 10 years in prison if convicted and a life ban from politics under the new military-drafted constitution.

Thousands of supporters are expected to turn up outside the court in northern Bangkok for the ruling in defiance of the junta's calls for people to stay at home.

Some 3,000 protesters are expected, deputy Bangkok police commissioner Major General Panurat Lakboon told reporters Monday.

"Police will deploy anti-riot forces to provide security... the total will be 4,000 officers," Panurat said.

Supporters would not be allowed to "invade the court vicinity" but would be permitted to gather nearby.

Yingluck's previous court appearances have seen increasingly large crowds gather outside the court, showering her with roses and chanting - a rare sight in a nation where political gatherings remain outlawed.

But her flagship rice scheme, to pay farmers nearly twice the market rate for their crop, was one of the policies which prompted large-scale protests against her administration.

The scheme handed billions of dollars to her rural voter base but also allegedly led to massive graft as brokers sold sub-par rice or declared inflated inventories to get the subsidy.

It left Thailand with huge stockpiles of unsold rice.

Throughout her trial Yingluck defended the scheme, saying she acted in good faith to raise the incomes of the poorest and was the victim of "a subtle political game".

The military and prosecutors say she must take personal responsibility for the scheme, in what is an unprecedented move to punish a Thai leader for a policy.

Analysts say the junta and its establishment allies are bent on crushing the political machine led by Yingluck and her billionaire brother Thaksin Shinawatra, who was himself ousted in a 2006 coup.

The siblings are beloved in Thailand's poor northeast but loathed by Bangkok's traditional elite, who hit their governments with coups or court rulings.

"Though a verdict against Yingluck would legally spell the end of her participation in Thai politics, such a ruling would draw Shinawatra supporters increasingly together against the junta," Paul Chambers, a Thai politics expert at Naresuan University, told AFP.