A 15-year-old French Muslim girl has missed school for two days this month in a dispute over her long black skirt, seen as going against France's law guaranteeing secularism.

A popular Twitter hashtag #jeportemajupecommejeveux (I wear my skirt as I like) popped up on Wednesday after the dispute was made public in the girl's local newspaper in Charleville-Mezieres, in northeast France.

The region's Academic Services said it backed the decision, stressing that the student was not excluded from school but was asked to change her clothes.

School officials want a dialogue with the family. Academic Services said the student insisted on the religious symbolism of her long skirt contravening the 2004 law banning headscarves and other "ostentatious" religious symbols.