No one has claimed responsibility for the attack, which took place in northern Gaza.
At least 30 Palestinians have been killed in fighting between rival groups Hamas and Fatah since Mahmoud Abbas, the Palestinian president, called last month for early presidential and parliamentary elections.
Earlier this week Palestinian factions including Hamas and Fatah resumed talks on forming a coalition government. Similar talks broke down last year.
Hamas has struggled to govern since taking office in March under the weight of US-led sanctions imposed because of its refusal to recognise Israel, renounce violence and abide by interim peace deals.
Fatah's Abbas and Hamas leader Khaled Meshaal held inconclusive unity talks in Damascus this week.