Lebanese armed group Hezbollah fired a salvo of rockets onto northern Israel on Monday in response to at least three of its members being killed in Israeli shelling on Lebanon.

The exchange of fire marks a significant expansion of the conflict between Israel and Palestinian militants to the Israeli-Lebanese border further north. Iran-backed Hezbollah and Israel fought a brutal month-long war in 2006.

Hezbollah in a statement on Monday said it had fired rockets and mortars on two Israeli military posts in the Galilee. The Israeli military said it identified a number of “launches” from Lebanon into Israel, without any injuries. It said it was responding with artillery fire onto Lebanon.

Hezbollah said in consecutive online statements that three of its members had been killed in Israel’s “aggression” on southern Lebanon on Monday afternoon. Two Lebanese security sources told Reuters two more Hezbollah members were killed.