A prosecutor has ordered the arrest of an Egyptian man whose 15-year-old son was detained last month for bringing a ruler with a Muslim Brotherhood symbol on it to school, the family's lawyer said.

The father, Mohamed Abdulghani Bakara, was accused of encouraging his son Khaled to bring the ruler to the classroom, the lawyer said, in a sign of a widening crackdown on the organisation since the army ousted former president Mohamed Morsi of the Brotherhood in July.

Lawyer Amr Abdel Maksoud told the Reuters news agency there was no legal basis for the charges and arrest warrants issued in the Nile Delta town of Kafr el-Sheikh.

"They (the prosecution) are helping the army dominate the country," he said.

Khaled remains in detention on suspicion of inciting violence, slandering the Egyptian army and membership of a banned group, legal sources said.

'Spreading chaos'

Two of the boy's teachers, Ashraf Raslan and Hamidou el Kheish, also faced charges of "spreading chaos among school students" by persuading him to keep the ruler, judicial sources said.

"It shows the targeting of people not even on the basis of membership (in the Brotherhood), but also based on perceived allegiance or affiliation," said Heba Morayef of campaign group Human Rights Watch.

She said the case is a way of intimidating voters ahead of the January 14 and 15 referendum on whether to accept the new constitution.

The vote on Egypt's constitution will replace the one passed under Morsi and pave the way for new presidential elections.

Security forces have killed hundreds of Brotherhood supporters and jailed thousands more since July. The Brotherhood has won every election since 2011, but was banned by an Egyptian court in September. 

Source: Reuters