A letter prepared by the Cabinet Secretariat to all deputy premiers said that during Thaksin's absence from work, Chidchai would assume authority, except when the need arose for Thaksin to perform such duties as head of government, the source said.

"The document shows Thaksin still has full authority and that he is ready to assume it any time he wants," the source said.

Copies of the letter, dated last Friday, have also been sent to other Cabinet members, state agencies, provincial governors and foreign embassies.

On Tuesday night last week, amid mounting pressure for him to step down, Thaksin announced in a nationally broadcast he would not accept the prime minister post in the next government.

According to the letter, Thaksin told the Cabinet at its special meeting on Wednesday last week that he was acting because he wanted to take a rest after five years of working non-stop. He also wanted unity among conflicting groups.

Chidchai has worked on Thaksin's behalf since the Thai Rak Thai party leader moved out of Government House on Wednesday last week.

Kasem Sorasakkasem, a legal expert from Chat Thai Party, yesterday said the Cabinet Secretariat's letter contained vague statements about Thaksin's reasons for taking a break.

Thaksin should have made it clear whether he was taking official leave, as he had not put it in writing, Kasem said.