Israel killed a top commander from the Iranian-backed Palestinian militant group Islamic Jihad in a rare targeted strike in the Gaza Strip on Tuesday, and militants responded by firing rockets at Israeli cities, including Tel Aviv.
In the most serious escalation in months, an Israeli missile attack also targeted the home of an Islamic Jihad official in Damascus, killing two people including one of his sons, Syrian state media said. Israel declined any comment on that incident.
"Israel executed two coordinated attacks, in Syria and in Gaza, in a declaration of war," Islamic Jihad leader Khaled Al-Batsh said at the Gaza funeral of Baha Abu Al-Atta.
Israeli officials described Al-Atta as a "ticking bomb" who was responsible for a string of recent cross-border rocket, drone and sniper attacks and was suspected of planning more.
"We conducted the attack [on Al-Atta] because there was no other choice," Israeli military spokesman Lieutenant-Colonel Jonathan Conricus said. "I want to emphasise that we are not looking to further escalate the situation."
Al-Atta's slaying, in his home along with his wife, looked likely to pose a new challenge for Gaza's ruling Hamas faction, which has mostly pursued truces with Israel since a 2014 war.
Israel casts rising Gaza tensions as part of a regional struggle with arch-foe Iran that has also played out in Syria. Conservative Israeli Prime Minister Benjamin Netanyahu has cited such scenarios in trying to form a coalition government with centre-left rivals after two inconclusive elections this year.
Islamic Jihad said the target of the Damascus attack was the home of a political leader, Akram Al-Ajouri. His possible significance to Israel was not immediately clear.