Thailand's junta leader Prayut Chan-O-Cha has said he may appoint his brother as next army chief, one of the most powerful jobs in the coup-prone kingdom.

Prayut, who is now prime minister, was the army chief in May last year when he seized power from an elected government which opponents had decried as corrupt and nepotistic.

He defended the decision to consider his sibling Preecha Chan-O-Cha, currently serving as an assistant army chief, for the top job.

The defence ministry is shortly due to submit its recommended candidate for the job. Preecha and the other assistant army chief, Teerachai Nakvanich, are the only two applicants.

"Why is it a problem that he is my younger brother?" Prayut told reporters in Bangkok on Tuesday when asked about the possibility of his sibling winning the role.

The position is pivotal in a country where the army plays a key political role -- Thailand has seen long stretches of military rule with 19 successful or attempted coups since 1932.

"Why would his appointment be damaging?" Prayut said in his trademark rhetorical style.

"He's never asked me for any favours. He's worked his way up himself," added the premier, dismissing speculation of a counter-coup against Preecha's appointment.

"I don't fear a counter-coup. I am happy to hand over power," he said.

An announcement on the new army chief is expected before the end of September, when current leader Udomdej Sitabutr is due to retire.

The coup ended months of often violent protests in Bangkok against the former government of Yingluck Shinawatra and brought with it a flurry of curbs on civil liberties, including a ban on political assembly and criticism of junta rule.

Prayut has said the coup was necessary to restore order and to curb corruption and cronyism -- labels attached to former governments led by or linked to the Shinawatra family.

The power grab was the latest act in an ongoing political saga that has gripped the country for nearly a decade since Yingluck's older brother and then-premier Thaksin Shinawatra was toppled by a 2006 coup.

The long-running conflict broadly pits the rural and urban working-class supporters of the Shinawatras against the royalist elite, bolstered by large sections of the military.

Thaksin was criticised for nepotism during his premiership for the appointment of his cousin Chaisit Shinawatra as army chief.