BANGKOK (AFP) - Thailand's junta chief Prayut Chan-o-cha on Tuesday (April 19) defended his brother against allegations of nepotism after a leaked memo revealed that the brother, who is a general, had secured a post in the military for his son.

Prayut's nephew will now serve as a sub-lieutenant in the army's department of civilian affairs, according to the document signed by the 25-year-old's father, an army general who is permanent secretary of defence.

Former army chief Prayut, who seized power in a 2014 coup and has vowed to stamp out corruption, insisted the appointment was lawful and reasonable.

"Today the offspring of military families are appointed (to positions) because they gain trust from what their parents have done for the country," the junta chief told reporters.

"Everything was legal and correct, that's it," he added.

His brother also defended the move in comments to local media, saying his son may lack a military background but is qualified for the post through his experience in public relations at an oil company.

The controversy, which has seen activists file complaints of nepotism to the state's anti-graft agency, comes weeks after thousands of parents across the country said farewell to sons recruited in the kingdom's annual draft.

Despite their self-styled reputation as graft-busters, the ruling generals have faced several corruption scandals since toppling an elected government in 2014.

Last year the military was forced to field a flurry of accusations over a multi-million dollar park which it built. There were claims of widespread kickbacks.

Internal probes into the park later declared it free of graft, though critics dismissed the findings as lacking transparency.

The junta stepped in two years ago amid mass protests against the government of Yingluck Shinawatra.

Her powerful political family is reviled by the kingdom's military-backed elite but loved in rural northern provinces for injecting money into poor farming villages.