Israel says it has launched air strikes against Hamas targets in the Gaza Strip after incendiary balloons were launched from the territory.
Explosions were heard in Gaza City in the early hours of Wednesday.
Several balloons, designed to cause fires, were sent from Gaza into Israel earlier on Tuesday.
It is the first major flare-up since a ceasefire on 21 May ended 11 days of fighting between the two sides.
In a statement, the Israel Defense Forces (IDF) said its fighter jets had hit military compounds operated by Hamas in Khan Yunis and Gaza City.
It said "terrorist activity" took place in the compound, and that the IDF was "prepared for all scenarios, including the resumption of hostilities, in the face of continued terror acts from the Gaza Strip."
It is not immediately clear if the air strikes have caused any injuries.
A BBC journalist in Gaza has shared a video on social media, saying that Israeli drones can be heard in skies over the territory.
The sound of #Israeli military drones can be heard , state of fear in #Gaza tonight as the Israeli airstrikes have renewed, Israeli warplanes attacked 2 #Hamas military sites in response to sending incendiary balloons that caused fires in southern #Israel. pic.twitter.com/yrTWikmiMX
— Rushdi Abualouf (@Rushdibbc) June 15, 2021
Israel's fire service said the incendiary balloons launched earlier from Gaza had caused at least 20 fires in fields by communities in southern Israel.
Hamas earlier threatened to take action over an Israeli nationalist march on Tuesday through occupied east Jerusalem.
Ahead of the march, local media reported that the Israeli military was on heightened alert. It also said Iron Dome missile defence batteries had been deployed to counter possible Palestinian rocket fire.
- BBC