The Israeli military says a missile was fired into Israel from neighbouring Syria early on Thursday, and that Israel has struck targets in Syria in response.
There were no immediate details on whether the missile landed in Israel or was intercepted.
Earlier, air raid sirens sounded in Dimona, home to Israel’s secretive nuclear reactor, indicating a possible incoming attack.
Israeli media also reported loud explosions in central Israel.
The reports came amid heightened tensions between Israel and its archenemy Iran.
Iranian authorities have blamed Israel for a series of incidents targeting Iran’s nuclear programme – including a mysterious fire that recently damaged its Natanz research site – and has vowed revenge.
Israel has not openly commented on the incidents, but has signalled possible involvement.
Israel accuses Iran of trying to develop nuclear weapons and has opposed US-led efforts to revive the international nuclear deal with Iran.
Iran says its nuclear programme is for peaceful purposes only, and has noted that Israel is widely believed to have a nuclear weapons program in Dimona.
Israel neither confirms nor denies claims it has nuclear weapons.