After being forced out of office in a 2006 bloodless coup, Thaksin is in self-imposed exile to avoid a two-year jail term on corruption and abuse of power conviction.
Wednesday's announcement came a day after a court issued arrest warrants for Thaksin and 12 other leaders of the pro-Thaksin group, United Front for Democracy against Dictatorship (UDD).
The UDD ended a three-week siege of Government House, the site of the prime minister's office, in central Bangkok to avoid a potentially bloody confrontation with troops on the same day.
Al Jazeera's Tony Cheng, reporting from Korat in northeastern Thailand on Wednesday, said military checkpoints had been established all over the country to prevent further unrest.
"They [the military] are very keen to ensure that if they see large buses of Red Shirt protesters heading back into Bangkok, they can stop them.
"The government has got the situation under control. All the Red Shirts have been bussed out of the capital, but they have said they are not going to give up," Cheng reported.
The government said Thaksin strengthened the will of red-shirted anti-government protesters by speaking to them via video almost nightly during the recent unrest, at one point even calling for a revolution.
The Red Shirts want Abhisit Vejjajiva, the current prime minister, to resign and call elections, saying that his rise to power is illegitimate.
Thai police said they were searching for the other protest leaders named in arrest warrants. Three have been charged and are in detention while the others remain at large.
The warrants accuse protest leaders of breaching the emergency measures put in place on Sunday, threatening acts of violence and inciting others to break the law.
The demonstrations left two people dead and 123 injured this week.