Deutsche Welle wrote that Israeli warplanes struck a target in the eastern Gaza Strip early on Friday in response to a rocket strike on a building in southern Israel in the most serious cross-border incidents in a month.

An Israeli army spokesman said Israeli Air Force warplanes struck targets belonging to Hamas militants. There were no immediate reports of casualties on either side.

The exchange has put in doubt a ceasefire reached in May after the most serious violence since 2014.

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."

Israel electioneering?

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. 

Israel is holding new elections in September after Prime Minister Benjamin Netanyahu failed to assemble a coalition last month.