Israel says it has carried out air strikes against Hamas militant targets in Gaza, in retaliation for incendiary balloons launched from the territory.
Explosions were heard in Gaza City in the early hours of Wednesday.
Several balloons were sent from Gaza into Israel earlier on Tuesday causing multiple fires, according to the Israeli fire service.
It is the first major flare-up since 11 days of fighting between the two sides ended in a ceasefire on 21 May.
It followed a march by Jewish nationalists in occupied East Jerusalem on Tuesday, which had drawn threats from Hamas, the militant group that runs Gaza.