Indonesia's education ministry Thursday strongly criticised officials in a small town in Aceh province for asking children to assess the size of their private parts in a graphic school survey, AFP reports.

The health questionnaire, distributed to 11- and 12-year-olds Tuesday at a school in the town of Sabang, contained pictures of genitalia and also asked whether students had experienced erotic dreams.

Nurlina said her 12-year-old son was asked to complete the survey, which showed images of both male and female private parts "from the smallest to the biggest, then asked the students which one most looks like theirs".

"That's just indecent," said the 40-year-old, who like many Indonesians goes by one name, adding that she stopped her son from filling in the form and complained to the school.

Officials had planned to distribute the survey to the six junior high schools in the town -- but only got as far as one before the pictures sparked outrage.

The head of Sabang education office, Misman, insisted the surveys had simply been to assess the health of students.

The official, who goes by one name, said he had no idea about the pictures -- which he described as "too vulgar" -- before parents complained.

He said a similar survey had been distributed last year but it did not contain the pictures.

Ibnu Hamad, a spokesman for the education ministry in Jakarta, said the government regretted the fact students had been asked about their genitals, and such questions were not normal in school surveys.

"It is totally unnecessary because there is no need to measure the size of students genitals for any purpose," he told AFP.

However, the ministry has not yet launched a formal investigation as officials in Jakarta were still trying to get in touch with Misman, he said.

The first page of the survey, a copy of which was seen by AFP, said it was aimed at "understanding your health" and supporting "the teaching process".

It is particularly surprising that the survey appeared in Aceh, one of the most conservative areas of Muslim-majority Indonesia and the only province in the country the enforces Islamic sharia law.