The Revenue Department has sent letters to banks and financial firms searching for assets belonging to Thaksin's son and daughter, Phantongtae and Pinthongta, said Mr Sanit Rangnoy, the head of the department.

'We expect to be able to seize those assets from those financial institutions from early December,' Mr Sanit told Reuters.

The seizure began after the department's appeal panel upheld a June ruling by an anti-corruption body set up by the ruling military, which ousted Thaksin in a bloodless coup last year.

The anti-graft committee ruled that Thaksin's children broke tax laws in the US$3.8 billion (S$5.5 billion) sale of telecommunications giant Shin Corp to Singapore's Temasek Holdings last year.

The deadline for the 12 billion baht back tax and fine payments had passed, allowing tax officials to start the seizure, Mr Sanit said.

The Shinawatra children, both directors of Manchester City football club which their father bought in July, could appeal against the Revenue Department's seizure order through the Tax Court, revenue officials said.

There has been no word from the Thaksin children yet.

The tax-free Shin sale outraged Thailand's urban middle-class voters who staged street demonstrations in Bangkok against it. The protests eventually led to the overthrow of Thaksin, winner of two landslide election victories.

Phantongtae and Pinthongta, both in their 20s, acquired the Shin shares at 1 baht each through an offshore company that Thaksin founded.

They then sold 329 million shares in Shin, which has interests in telecommunications, satellites and television, to Temasek at 49.25 baht each.

Thaksin, who lives in exile in London, has always insisted the Shin sale satisfied all the rules in Thailand, where share sales carried out through the stock market are not taxed.

The former premier and his wife Pojaman have also been summoned home to answer corruption charges.

They are accused of failing to disclose their assets - as required of public officials under Thai law.

Other members of Thaksin's circle have also been investigated for corruption and tax evasion.

Pojaman's brother Bhanapot Damapong and her secretary were charged with tax evasion in March.

REUTERS