An Indonesian school has expelled a 14-year-old girl, claiming she "tarnished" the institution's image after she was raped by a trafficking syndicate, a child rights activist said on Tuesday.

Arist Merdeka Sirait, chairman of the National Commission for Child Protection, said a private school just outside Jakarta expelled the teenager during a ceremony attended by pupils on Monday.

A teacher told the girl she had "tarnished the school's image", said Sirait. "The school has worsened her trauma by humiliating her in front of hundreds of schoolmates," he said.

The commission has sent a letter of protest to the school's management and will also write to the education ministry, asking them to review its licence, said Sirait.

"The girl was the victim of child trafficking. The school should have helped her to cope with her trauma," he said.