Protesters are demanding Mr Thaksin's resignation
Thousands of people have marched on the Singaporean embassy in Bangkok in the latest of a series of protests aimed at ousting the Thai prime minister.
Thaksin Shinawatra's opponents are particularly angry about a tax-free sale of his family's stake in a Thai telecoms giant to a Singapore company.
The latest protest came as Thailand's election chief reportedly said he could not postpone a controversial poll.
Mr Thaksin called the snap election for 2 April in a bid to regain legitimacy.
Election Commission chairman Vasana Puemlarp last week cast doubt on whether the poll could go ahead due to a vow by the main opposition to boycott the election, leading to concerns over whether enough MPs could be returned to fill parliament.
But on Tuesday he told a Bangkok radio station that such a ruling was not within his powers, according to Reuters news agency.
"The law doesn't allow me to set the election date," he reportedly said, adding that only the prime minister could make that decision.
Mr Thaksin is campaigning hard in rural areas
There are particular concerns about the election in two-thirds of the constituencies where the ruling Thai Rak Thai party would be unopposed if the election boycott goes ahead, as candidates need to win 20% of the available vote to be elected.
This could be a problem in the restive south, where the party's unpopularity in the face of a long-running insurgency meant the party did not win a single seat in the last election in February 2005.
On Sunday, the main opposition Democrat Party alleged that Thai Rak Thai officials were involved in a plan to hire candidates to stand for small opposition parties to get round this problem.
The Election Commission has pledged to look into the claims, and on Tuesday said it had ordered the transfer of the three officials in question pending an investigation.
Traffic came to a halt in Bangkok's commercial district on Tuesday as the marchers moved towards the embassy chanting "Thaksin get out".
"I politely ask Singapore to stop cooperating with Thaksin to loot Thailand," protest leader Sondhi Limthongkul told the crowd, calling the deal "economic imperialism".
Mr Thaksin, who denies any wrongdoing, continued his campaign in rural areas, where he is still popular.
Addressing a crowd in the northern city of Chiang Rai on Monday evening, he criticised the protest leaders.
"They want a new government, but they forget that there is big support for this government," he told a cheering crowd.
See more images of the protests.