A rocket fired from Lebanon has crashed into northern Israel, the army says, without any immediate reports of injuries.
"At least one rocket fired from Lebanon hit the Upper Galilee," a message on the military's official Twitter feed said.
Israeli artillery returned fire, Israeli security sources said.
It was the third consecutive day in which Israel came under rocket fire from the north as well from the Gaza Strip in the south.
Five rockets from Syria hit the Israeli-occupied sector of the Golan Heights on Sunday and the day before a rocket was fired from Lebanon.
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There were no casualties in any of those attacks and no Israeli fire in response.
Last month, a rocket fired from Syria prompted Israeli artillery to shell Syrian army positions.
And in June, Israeli warplanes attacked Syrian military headquarters and positions after an Israeli teenager was killed in what the Jewish state said was a cross-border attack by President Bashar al-Assad's forces.
Other previous incidents have been put down to stray fire from clashes between Syrian government troops and rebels.
