CAIRO (Reuters) – Twenty people were injured in a village clash that erupted over a love affair between a Muslim man and Christian woman who went missing for two weeks, security sources said on Saturday.

Police arrested 13 people in connection with the clash late on Friday and heightened security in the village near Mahalla el-Kubra, a city in Egypt’s northern Nile Delta area, for fear of further violence, the security sources said.

Relations between Egypt’s majority Muslims and its Christians, mainly Copts, are usually calm but can become strained and sometimes erupt into violence over issues such as women and land.

The Christian family in el-Touma village said one of their members, a 19-year-old woman, had been having an affair with a 25-year-old member of a Muslim family and accused the man of being behind her disappearance for two weeks, the sources said.

The clashes erupted after the young woman returned and the fighting involved sticks, knives and swords, the sources added.

Christians make up about 10 percent of Egypt’s roughly 76 million people.