The Israeli military claimed at least three of those killed were militants linked to Hamas' armed wing, Ezzedine al-Qassam Brigades.
Troops and tanks had earlier pushed across the border into central Gaza, where they became locked in heavy clashes with Palestinian militants.
Although Israel has vowed to bolster Palestinian President Mahmoud Abbas and his new Western-backed emergency government, it has also vowed to continue attacks on militants.
Mr Abbas sacked the Hamas-led unity government last month in a crisis that saw the Islamists seize control of Gaza while Mr Abbas' Fatah party retained its West Bank power base.
