Outgoing Deputy Prime Minister Wissanu Krea-ngam said on Wednesday he cannot say whether Thaksin Shinawatra's formal application for a royal pardon has been filed.

He could only confirm the application has yet to reach him, Mr Wissanu said.

"The royal pardon application has not reached me yet. And I can't say if it has been submitted because I really don't know," he said.

On Tuesday, Thaksin's lawyer said documents required to support the royal pardon application were being prepared for Thaksin, who is facing eight years in prison in three cases.

Normally, such a royal pardon application is submitted by the inmate himself to the prison warden, who then forwards it to the Department of Corrections, Mr Wissanu said.

The department is then responsible for considering forwarding the application to the justice minister, who would ask the prime minister to submit the application for royal approval, he said.

Asked who is likely to get Thaksin's royal pardon application request -- Gen Prayut Chan-o-cha, the outgoing prime minister, or Srettha Thavisin, the newly elected prime minister -- Mr Wissanu said if the application reaches him now, it will be forwarded to Gen Prayut, the caretaker prime minister.

However, he said, as soon as the new cabinet takes office, the royal pardon application will be forwarded to Mr Srettha.

In another development, political activist Srisuwan Janya petitioned the Ombudsman to probe state officials allegedly giving Thaksin preferential treatment.

"Since Thaksin returned on Aug 22 to Thailand from years of self-imposed exile abroad, he has been offered special treatment as if he were an important person while in reality, he is a fugitive," said Mr Srisuwan.