The Israeli strikes targeted an open area in northern Gaza and a militant training site belonging to the strip's Hamas Islamist rulers in southern Khan Yunis, Palestinian security sources told AFP.

The strikes came after Israel cut by half the fishing zone off the blockaded coastal territory, a common response following projectile attacks by armed groups in Gaza.

Israel's army had no immediate comment on the strikes.

But the military branch responsible for civil affairs in the Palestinian territories (COGAT) said the fishing zone had been reduced from 12 nautical miles to six.

"The decision was made following the continued launching of incendiary balloons from the Gaza Strip towards Israel, which constitutes a violation of Israeli sovereignty," it said in a statement.

Hamas was "responsible for all activities within the Gaza Strip and all actions originating in the Gaza Strip directed towards the state of Israel", COGAT said.

"It will therefore bear the consequences for the violence committed against the citizens of the state of Israel."

Earlier Sunday, Israeli firefighters said they extinguished brush blazes at three spots in the Eshkol region near the border, blaming blaming "incendiary balloons" as the cause.

The balloons are basic devices intended to set fire to farmland surrounding the Israeli-blockaded Palestinian enclave.

On July 12, Israel announced it was re-expanding the fishing zone off Gaza and allowing additional imports into the Palestinian territory but warned the measure could be reversed in response to fresh unrest.

An 11-day conflict in May saw Israel launch hundreds of air strikes on Gaza, and Hamas fire thousands of rockets at Israel.

Prior to the May conflict, the Gaza fishing zone was 15 nautical miles, but Israel reduced it during the warfare.

There has been sporadic unrest since a ceasefire ended the conflict, with incendiary balloons launched from Gaza and Israeli reprisal air strikes targeting facilities belonging to Hamas. No casualties have been reported.

The last time balloons from Gaza caused a fire in Israel was early this month.