Israel has said Lebanese forces fired the first shots in a clash on the border and warned of “consequences” if the incident is repeated.

Lebanese officials claimed they had only fired “warning shots” because Israelis had been trying to cut down a tree in Lebanon. But Israel said its soldiers “were on routine activity in Israeli territory”.

An IDF spokesman said: “The soldiers were in an area that lies between the "blue line" (the internationally recognised border between Israel and Lebanon) and the security fence, thus within Israeli territory.”

Israel described the attack as “a severe violation of UN Security Council Resolution 1701” and said it would file a protest with the UN Secretary General and the Security Council.

The spokesman added: “Israel holds the Lebanese government responsible for the grave incident that disrupted the calm in the region.”

Unconfirmed reports suggest four Lebanese soldiers were killed in the fighting. Israel said they had damaged several of the Lebanese forces’ armoured combat vehicles

The flare-up is the biggest interruption to peace in the Galilee border region since the Second Lebanon War of summer 2006.

The UN appealed for both countries to exercise "maximum restraint".