Former prime minister Thaksin Shinawatra has undergone surgery and is in the process of recovery according to his daughter Paetongtarn, who said on Tuesday she does not know how long he must remain in hospital.

Thaksin had the operation last week and had yet to recover. His blood pressure was good some days, but not so good other days, she said.

Ms Paetongtarn did not give further details. She said reporters should ask Thaksin's doctors.

She said she really had no idea on how long her father would have to stay in hospital.

A chief physician at Police General Hospital on Tuesday confirmed Thaksin had undergone surgery for several reasons.

On Monday, activists demanded an update on Thaksin's health, saying he had spent the last month in Police General Hospital, having been admitted almost immediately after he was sent to prison, where he is serving a one-year sentence.

Ms Paetongtarn said that her family was considering applying for parole for Thaksin.

On Monday the Department of Corrections said that Thaksin would have to serve at least six months in prison before applying for a parole, or until late February.

The department will also decide if Thaksin needs continuous medical treatment outside prison.