Incident follows exchange of rocket fire between Israel and Hamas on Thursday in most serious escalation since May.

Israeli warplanes have attacked several Hamas targets in the Gaza Strip following a Palestinian rocket attack in the south of Israel, the military has said.

The incident comes after Israel and Hamas exchanged rocket fire on Thursday, in the first serious cross-border escalation since a surge in fighting in May.

In a statement on Friday, the Israeli military said fighter jets struck “infrastructure in military compounds and a Hamas naval force military compound as part of a strike on a number of Hamas terror sites throughout the Gaza Strip”.

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The statement said the attack came in response to a rocket launched from Gaza which hit a Jewish seminary in the town of Sderot.

The seminary was empty at the time of the attack as students had left to celebrate the Jewish Sabbath with their families.

“If the rocket had hit a few hours earlier there would have been a disaster,” former Defence Minister Amir Peretz, a Sderot resident, said in an interview with Israeli public radio on Friday.

No casualties were reported on any side.

‘We will respond’

Speaking from the Gaza Strip, Abdellatif al-Qanoo’, a spokesman for Hamas, told Al Jazeera the rocket fire was in response to Israeli aggression.

“The occupation [Israel] is bearing the fruit of its own escalation, continuous attacks [on Gaza] and its stalling in implementing agreements between us.

“Our people will continue to challenge the occupation. We will respond to this behaviour [Israeli attacks] by continuing to gather and march,” added al-Qanoo’ in reference to planned protests along the Israeli-Gaza border on Friday.

The latest escalation followed Israel’s closure of offshore waters to Gaza fisherman on Wednesday in what it said was a response to incendiary balloons launched across the frontier that caused fires in fields in southern Israel this week.

“Due to the continuous launching of incendiary balloons and kites from the Gaza Strip towards Israel, it has been decided tonight [Wednesday] not to allow access to Gaza’s maritime space until further notice,” Coordination of the Government Activities in the Territories (COGAT), the Israeli defence ministry department responsible for Palestinian civil affairs, said.

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A spokesman for the Israeli fire service said incendiary balloons from Gaza caused seven fires on Tuesday alone. In the past year, Palestinians have set fire to a number of areas of farmland in southern Israel.

May violence

In two days of heavy fighting in early May, Israeli raids killed at least 25 Palestinians, more than half of them civilians, according to Gaza health authorities. In the same period, projectiles from Gaza killed four civilians in Israel, local health officials said.

A truce mediated by Egypt, Qatar and the United Nations ended that round of violence.

Some two million Palestinians live in Gaza, whose economy has suffered years of Israeli and Egyptian blockades as well as recent foreign aid cuts and sanctions by the Palestinian Authority, Hamas’s rival in the Israeli-occupied West Bank.

Israel says its blockade is necessary to stop arms reaching Hamas, with which it has fought three wars since the group seized control of Gaza in 2007, two years after Israel withdrew its settlers and troops from the small coastal enclave.