The latest conflict was sparked on Wednesday when Israel closed offshore waters to Palestinian fishing boats after incendiary balloons had set fire to Israeli farmland.
"Due to the continuous launching of incendiary balloons and kites from the Gaza Strip towards Israel," the Israeli Defense Ministry said, "it has been decided tonight [Wednesday] not to allow access to Gaza's maritime space until further notice."
Early Thursday, Israeli fighter jets hit a tunnel in Gaza after air defenses intercepted an incoming rocket.
There was no claim of responsibility for the rocket or incendiary balloon attacks.
Hamas spokesman Hazem Qassem accused the Israelis of using the situation for electioneering. The threats against the Gaza and Hamas leaders were "only to gain more electoral votes," Qassem said.