Prime Minister Surayud Chulanont said yesterday a graft probe into ousted predecessor Thaksin Shinawatra could be wrapped up by the end of this month and he was confident it would "pin him down".

Several days ago prosecutors charged Thaksin's wife Pojaman and her brother Bhanapot Damapong with tax evasion, and on Tuesday a sub-panel of the Assets Examination Committee ordered his two children, Panthongtae and Pinthongta, to pay tax of Bt10 billion in connection with the sale of Shin Corp.

Beside charges of tax evasion, a number of allegations - including a scandal over the purchase of land on Ratchadapisek Road, loans from the Krung Thai Bank and irregularities behind baggage scanners for the new airport - have been raised against the ousted premier since the September 19 coup.

"I can say that we are closing in on the final chapter of Mr Thaksin's future," Prime Minister Surayud Chulanont told a news conference in Tokyo. "We have all the evidence and I think the investigation ... will be able to pin him down this time," Surayud said.

He said he told a senior Justice ministry official he needed the investigation to be finished "maybe by the end of April" but that he would not "violate the rule of law" in rushing the case.

"We move maybe a little slowly," he said. "I don't want to rush because we will be blamed by other people that we didn't take a close look at the investigation process."

Surayud insisted the government was not preventing Thaksin from returning but added that now may not be the "appropriate time" for the former premier to do so.

He said Thaksin's decision to remain abroad was related to the refusal of the Thai people to forgive him for the damage he had done to the country.

Surayud, who was in Tokyo to sign a free-trade agreement, acknowledged that last year's coup caused concern in Japan - Thailand's top investor - but said the "peaceful military intervention" had been necessary.

The coup's "triggers" were "the unprecedented consolidation of political and financial power by Thaksin during his five years as prime minister, his alleged abuse of state power, widespread corruption, curtailment of media freedom and a disastrous human rights record," Surayud said.

In his speech to the Japan National Press Club yesterday, Surayud said: "By the end of this year, following free and fair elections, Thailand will again emerge with enhanced democratic credentials and with stronger institutional foundations capable of delivering a better, more sustainable future for the majority of its citizens."

Surayud said the promulgation of the 1997 "Peoples' Constitution" coincided with "one of the most traumatic events in Thailand's modern history, the financial crisis of 1997, which cost our country nearly a decade of socio-economic development.

"Together, these two coincidental events set the stage for nine years of political and economic developments, which culminated in last September's peaceful military intervention," he said.

Surayud defended the military's decision to launch the coup, which he referred to as "time out" because for the first nine months of last year, the country was without an effective government.

"A general election was boycotted by the opposition, and later ruled invalid by the courts. Bangkok witnessed almost daily demonstrations against Mr Thaksin. The system of checks and balances had been subverted and we seemed to have exhausted all constitutional means to end the political impasse," he said.

"I believe this intervention was in the public interest and it certainly met with widespread public approval, as indicated by public opinion polls undertaken shortly after the event," he said.

Surayud said the interim constitution had set a very tough timeline for the restoration of democracy, and that the draft constitution was nearing completion and preparations were underway for a national referendum on it, due to be held in September.

The interim government and the Council for National Security were "absolutely committed to a general election, either on December 16 or 23."

Surayud also touched on the violence in the deep South, saying it was "deeply troubling to all Thais". He said he was "under no illusions" this crisis could be resolved quickly.

"If we consider this area's long history of neglect and coercion, exacerbated by today's global geo-political realities, which have nurtured a resurgence of fundamentalist religious thinking as a defence against perceived threats against religious beliefs, one begins to understand the difficulties we face.

"However, following on from my earlier apology to the citizens of this area, I intend to continue pursuing a policy of reconciliation, of increasing economic opportunities and of building ever closer relations with our neighbours, Malaysia and Indonesia."

Surayud also brushed off allegations his government had been slow in cracking down on Thaksin and his cronies.

"Some people have urged the use of executive power to short circuit the judicial process. But if we adopt that approach, how will the rule of law ever be strengthened?" Surayud asked.