Thailand's junta leader on Thursday said fugitive ex-premier Yingluck Shinawatra is in Dubai, a day after she was handed a five-year jail term in absentia for negligence.

Prayut Chan-O-Cha's first clear comments on Yingluck's whereabouts came a month after she ghosted out off Thailand, ducking a court ruling over charges she failed to stop graft and losses in a costly rice subsidy policy by her government.

On Wednesday Thailand's top court sentenced her in absentia to five years' jail, pulling the plug on her political career.  

She maintained her innocence throughout the case, which she said was a political fit-up sculpted by her family's enemies among the arch-royalist army and elite.

"I learned from the foreign ministry that now she is in Dubai," said Prayut, who toppled Yingluck's government from office in a 2014 coup.

Once a fresh arrest warrant is issued, Thai authorities may proceed with extradition efforts, he told reporters.

Yingluck's older brother Thaksin, also a former premier, has a home in Dubai.

The 2001 rise of Thaksin, a billionaire former cop with a magic touch at the polls, rattled Thailand's establishment and the country has since see-sawed between elected governments and coups. 

He fled Thailand in 2008 to avoid jail on a graft conviction he says was politically motivated.

Defence Minister Prawit Wongsuwan, a key architect of the coup that took down Yingluck's government, said "it's good she is in Dubai."

"Although don't have extradition treaty... Dubai officials informed our foreign ministry that they will not allow Yingluck to make any political move."

The 50-year-old, who still has the right to appeal, has not appeared in public since pulling the vanishing act on August 25, her initial ruling date.

The Shinawatra siblings lie at the centre of a political battle that has chewed at Thailand for more than a decade.

Shinawatra-backed parties have dominated electoral politics since 2001, enraging Bangkok's military-allied elite.

Unable to beat the Shinawatras at the polls, their rivals have turned to court rulings and coups to repeatedly knock their governments from power.