The Israeli army said it launched an operation dubbed "Northern Shield" to destroy "attack tunnels" it accused the Iran-backed Lebanese militia of digging under the border.

Hezbollah had not yet reacted and the United Nations Interim Force in Lebanon said that there no signs of any increased tension, as Israeli bulldozers went to work.

"The situation in UNIFIL's area of operation remains calm," Malene Jensen, a spokeswoman for the UN mission which monitors the border region, said in a statement.

"UNIFIL is liaising with all relevant interlocutors to ensure that the parties use the UNIFIL liaison and coordination mechanisms to maintain the continued calm and stability," she said.

In 2006, Israel and Hezbollah fought a devastating month-long war during which the Shiite group made extensive use of a network of tunnels to counter Israeli troops.

It has since boasted re-building its tunnel network but never clearly stated they were to be used for cross-border attacks.

Israel appears increasingly concerned that Iran is attempting to transfer some of its military influence from Syria, where Russia is the government's top ally, to Lebanon.

Near the Lebanese village of Kfar Kila, an AFP photographer on Tuesday saw at least one Israeli bulldozer churning up earth, apparently as part of Operation Northern Shield.