BANGKOK (REUTERS) - A lawyer for ousted Thai prime minister Thaksin Shinawatra said on Wednesday (March 22) there were no grounds for a new tax claim against him over the sale of shares in a telecoms company over a decade ago.

The military government has said its revenue department is estimating the tax amount and will have finalised the figures before a March 31 deadline to file a claim over the sale of shares in Shin Corp to Singapore's Temasek Holdings.

Thai media have estimated that the tax claim could be up to 16 billion baht (S$646.2 million).

Allies of Mr Thaksin say discussion of a new tax claim is politically motivated. He has lived in exile since being overthrown in 2006 to avoid corruption charges, but his populist movement remains at the heart of political division in Thailand.

A court ruled against an attempt by tax authorities to claim 12 billion baht on the share sale from Mr Thaksin's children in 2010, said Mr Thaksin's lawyer Noppadon Pattama. The court said they could not be taxed because the shares were owned by Mr Thaksin and his wife, he said.

Mr Noppadon said that the sale of the shares was tax exempt because it was done through the stock exchange.

"These are the basic arguments which are very powerful and enough to take care of the whole issue," he told reporters in Bangkok. "Dr. Thaksin hopes that he will get fair treatment regarding this issue in accordance with the law... Dr. Thaksin believes the strict enforcement of the rule of law will lead to reconciliation."

Prime Minister Prayut Chan-o-cha told reporters on Tuesday that due process would be followed in any tax claim.

The army overthrew a government led by Mr Thaksin's sister Yingluck Shinawatra in 2014 in the name of ending political turmoil.

Last month, the junta started reconciliation hearings with political parties ahead of elections that could happen as early as next year, but those talks do not touch on Mr Thaksin's fate.