A 28-year-old maths teacher has been arrested for making sexual approaches toward underage girls and possessing child pornography, the public prosecution department said on Thursday.

The man approached pupils at various schools in the Rotterdam region where he worked, the department said. He also gave extra tuition to pupils outside school hours.

The department said he approached his victims, who range in age from 12 to 16, by sending them sexually-charged messages on social media or via email. In some cases he persuaded them to send him films or photographs of themselves in sexual poses. It is not clear if he had actual physical contact with them.

The man was picked up last month for the assault of a minor some time ago. When police examined his computer equipment, they found chats and photographs of several girls, leading to the new investigation.

Two girls have since come forward to make a complaint but police suspect there may be many more.