Thai Prime Minister Thaksin Shinawatra has accused several military officers of plotting to assassinate him.
Police found the car near Mr Thaksin's home
He was speaking a day after police said they had intercepted a car containing bomb-making materials near his house.
A former army officer was arrested shortly afterwards and Mr Thaksin has also sacked the head of Thailand's main counter-insurgency operation.
But critics of the prime minister have expressed scepticism about the alleged plot.
Some have even claimed the whole incident could have been a stunt by Mr Thaksin or his supporters, to gain sympathy or divert attention from criticism of his leadership style.
According to the BBC correspondent in Bangkok, Jonathan Head, if this does turn out to be a real assassination plot within the armed forces, it would be an alarming development.
Thailand has a long history of coups and attempted coups, but the military has largely stayed out of politics for 14 years.
More arrests likely
This is not the first time Mr Thaksin has claimed that plotters have been trying to assassinate him, but few such claims have been taken seriously.
Thursday's discovery, though, is being treated by both the prime minister and the police as a serious attempt on his life.
"There are three to four military officers involved in the assassination plot," Mr Thaksin told reporters on Friday. "We know which group made [the bomb] and more suspects will be arrested."
Police said they found powerful bomb-making materials in the back of a car near Mr Thaksin's home early on Thursday morning.
They arrested the driver of the car, who turned out to be an employee of General Panlop Pinmanee, the deputy chief of the powerful Internal Security Operations Command.
Gen Panlop, who has now been sacked, has publicly denied any involvement in the incident.
Mr Thaksin believes someone was trying to assassinate him
As a former military death squad leader, he told reporters: "If I had done it, I guarantee that the prime minister wouldn't have survived."
Gen Panlop pointed the finger of blame back at the premier. "I think Thaksin cooked the thing up to damage me," he said.
He is not the only person to claim the bomb scare could have been a political stunt.
"The information disclosed by the authorities so far still has not convinced the public there was a real plot," Ong-Art Klampaiboon, a spokesman for the opposition Democrat party, told Reuters.
The newspapers were also sceptical. "Bomb plot or stunt?" the Bangkok Post asked in a front page headline. "Is this incident fact or stage-managed?" questioned the Thai language Post Today.
Mr Thaksin's supporters, though, are insistent that a real threat exists.
"There is a movement to bring the government to collapse and to kill the government's leader," said Defence Minister General Thammarak Isarangkun.
Countdown to election
Even before Thursday's incident, security around Mr Thaksin has been tight.
The country is preparing for a general election on 15 October - a re-run of a controversial poll in April, which was annulled because of an opposition boycott.
Since the April poll, the country has been in political limbo - divided between Mr Thaksin's supporters, in the rural hinterland, and his detractors, many of whom live in Bangkok.
In recent days there have been a series of minor scuffles between the two sides, in which several people have been injured.
Analysts had hoped that the October election might bring back some sense of normalcy and calm to Thailand's political scene.
But incidents like Thursday's bomb plot - whether real or not - show just how deep tensions still run.