BERLIN (AFP) - A German state has banned Facebook contact between students and teachers, citing the social media network's storage of personal data for commercial purposes, officials said on Tuesday.

Teachers chatting with students online and giving them access to photos and personal information also jeopardises professional distance, cautioned a message on the policy sent to teachers this week in Rhineland-Palatinate state.

"More and more, in certain schools, there are teachers and students who talk about school-related topics over Facebook, and we do not want that," state education ministry spokesman Wolf-Juergen Karle told AFP.

These conversations should happen over secure online educational platforms instead, Mr Karle said.

The state's education ministry also said Facebook's business model of collecting personal data for commercial purposes is not compatible with the educational mission of the state's schools.

Other German states have implemented or are considering measures restricting contact between students and teachers on social media networks.

Saxony announced this summer it is working on such regulations.

In Schleswig-Holstein, teachers have been barred from planning school trips or giving out grades on social media networks, national news agency DPA reported.

In 2011, the US state of Missouri passed a law banning Facebook contact between students and teachers.

The law never took effect, however, and was ultimately repealed after a teacher's union challenged it in courts, media reports said at the time.