Two children and a woman were killed after a shell fell on their house in a village in Sheikh Zuweid city, which featured deadly fighting earlier this week between militants and army forces, the sources added.
A 13-year old girl and a woman were injured in the incident.
In a separate incident, a roadside bomb targeting police and army vehicles killed a five-year-old child in the town of Rafah that borders the Palestinian Gaza Strip.
In another incident, two civilians were killed and one person injured in an explosion that took place after a mortar shell hit a power station in North Sinai.
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The station generates power to Sheikh Zwied, Rafah, some areas in east Al-Arish and the power line that leads to Gaza Strip.
On Wednesday, the government launched airstrikes against militants in retaliation to a wave of simultaneous suicide attacks on army checkpoints in the restive Sinai Peninsula, killing at least 70 people, mostly soldiers, in the biggest assault and triggering a massive retaliatory strike by the military using troops and F-16s.