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.
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.
According to reports, 205 militants have been killed in army raids in the past three days since the bloody attack in North Sinai.