The Israeli military denied any firing in the area but said that two mortar rounds were launched from Gaza overnight.
No Palestinian faction has claimed the dead fighters as its members.
Israeli forces have repeatedly raided areas in the east and south of Gaza during the past few days.
Attacks by Palestinian groups in Gaza and Israel have continued despite separate unilateral ceasefires declared on January 18.
The ceasefires followed Israel's 22-day offensive in Gaza during which about 1,300 Palestinians were killed.
Thirteen Israelis died during the same period due to the offensive or because of Palestinian rocket fire into Israel.