The police chief has been criticised by the government and military for failing to make progress in solving the New Year's Eve bombings in Bangkok which killed three people and wounded about 40.
The military-appointed government has repeatedly said it believes that Thaksin supporters were behind the bombings, but police have been reluctant to endorse the theory.
Instead, they have said that Muslim separatists, who have been fighting in the south, may have been responsible.

Thirteen people were injured in three
blasts in Thailand's south on Monday [EPA]
Meanwhile, violence continued in the south on Monday, with 10 soldiers injured in two roadside bomb blasts in Narathiwat province.
A third explosion in neighbouring Pattani province in the country's Muslim majority south injured three civilians.
Separately, results of a poll released on Monday showed that Surayud’s popularity had fallen below 50 per cent for the first time since he was appointed prime minister by the military in the aftermath of the coup against his predecessor on September 19.
The slump in the administration's popularity was due to its preoccupation with pursuing graft investigations against Thaksin rather than trying to solve the country's problems, including the violence in the south, the poll results suggested.