At least 12 people were injured in clashes in Upper Egypt when a group of Muslims attempted to stop Christians converting a house into a church.
Security officials said the Muslims set fire to building materials for the building in Odaysat, near Luxor.
Several members of both communities were reported injured in the subsequent clashes, as well as two policemen.
It is the latest in a series of violent sectarian incidents in Egypt in the past few months.
A security source quoted by Reuters said the Christians did not have official permission to build the church.
Police arrested 10 young men and the owners of the house, reports say.
Correspondents say curbs on building churches have been one of the main grievances among Copts, although these restrictions have been eased recently by presidential decree.
The Coptic Christian community is believed to make up 10% of Egypt's population of about 70 million.