Four children and a woman were killed Friday when a mortar round crashed into their home in North Sinai, where the Egyptian army is battling jihadists, officials said.
Security and medical sources said the woman and the children, aged between six and 16, died in Sheikh Zuweid, near North Sinai's main town of El-Arish.
It was unclear which side fired the mortar round, a type used by both the army and militants.
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Five civilians were killed Wednesday in a similar incident in the same area.
North Sinai is a bastion of the "Sinai Province" jihadist group. Formerly known as Ansar Beit al-Maqdis, it changed its name when it pledged allegiance to the Islamic State group in November.
On July 1, the group carried out a series of attacks on security forces in Sheikh Zuweid that the military said killed 21 soldiers.
The jihadists say their attacks are in response to a crackdown launched by the authorities after Islamist president Mohamed Morsi's ouster, which has seen at least 1,400 people killed and thousands more jailed.