Security forces in the Upper Egyptian city of Luxor have reportedly arrested five out of 10 male relatives accused of killing three female family members after suspecting them of having affairs.

An Egyptian security official said 10 male relatives have killed a mother and her two daughters on suspicion of moral offences — so-called "honour killings."

Head of Luxor security directorate Khaled Mamdouh told Al-Ahram Arabic-language news website that a 45-year-old company employee called Khaled had called the police to report that his mother and his two sisters had been missing, but he later withdrew the complaint, claiming the former had returned home.

The official said Friday the men suspected the three women of having affairs, and killed them to protect the family's honour. The three bodies were found in the Nile River near the ancient city of Luxor. They were wrapped in blankets and weighted with stones.

The official spoke on condition of anonymity because he was not authorised to speak to reporters.

Security forces were able to extract the body of the elder sister Friday afternoon as the search continues for the remaining two bodies.

"Honour killings" are common in Egypt, especially in the conservative southern region where women are often killed if caught in extramarital relations for bringing shame on their families.

The practice is against Egyptian law, and perpetrators are prosecuted if they are arrested.