The protest leader, Suthep Thaugsuban, a deputy prime minister in the previous government, told thousands of supporters occupying a state office complex late on Thursday that "the end game will happen in the next day or two".
Yingluck has ruled out resigning or dissolving parliament, and appears intent on riding out the storm. As tension mounts, her government has urged its supporters and the police to avoid confronting the demonstrators, who it says are running out of steam.
"The government will not instigate a violent situation because that is exactly what Suthep wants," said Udomdet Rattanasatein, a lawmaker from Yingluck's Puea Thai party.
"We will not be provoked."
(Read more: Spotlight on Thailand as political strife escalates)
Yingluck had governed for two years without a major challenge until last month, when her party tried to ram through an amnesty bill that would have expunged Thaksin's 2008 graft conviction and cleared the way for his political comeback.
The Senate rejected it, and Yingluck then shelved it, but the protests escalated, switching from a campaign against the amnesty to a bid to bring down the government.
Thaksin's working-class support has ensured parties led by him, his brother-in-law and now his sister have won a decade of elections. But Thaksin's opponents attempted to overthrow all of those governments, saying he politicized and bought-off the poor with cheap credit and healthcare and wasteful state subsidies.
Among the key protagonists in Thailand's dysfunctional democracy are those who revile Thaksin's authoritarianism - conservative generals, aristocrats, big businessmen and royal advisers - whose accusations of graft and disloyalty to the monarchy have mobilized Bangkok's middle class. Thaksin refutes those accusations.
The demonstrators have a presence at five locations in Bangkok, three in its historic heart, one in the city's northern fringe and another at the Finance Ministry, which they have occupied since Monday.
(Read more: Thai Finance Ministry occupied amid huge anti-government protests)
The Civil Movement for Democracy, as the anti-government demonstrators call themselves, has garnered support from white collar workers and 45 unions with a combined 200,000 members.
The union of Thai Airways International, 51 percent owned by the Finance Ministry, on Thursday threatened to go on strike and ground the flag carrier's fleet if any demonstrators were harmed.
"If the government uses force ... we will increase the pressure by stopping the plane wheels from turning," said the union's president, Damrong Waikanee.