The Israeli air force has launched an air raid on Hizbollah positions in southern Lebanon after Hizbollah guerrillas attacked Israeli posts hours after Israel assassinated Hamas leader Sheikh Ahmed Yassin in Gaza.
The frontier violence erupted at the Israeli-occupied Shebaa Farms, which Hizbollah says is Israeli-held Lebanese territory. The United Nations regards the area as occupied Syrian land.
Israeli security sources said Hizbollah fired anti-tank missiles and mortar bombs at Israeli forces. There were no immediate reports of casualties.
The border has been quiet recently but there have been sporadic flareups since Israeli forces withdrew from southern Lebanon in 2000 after a 22-year occupation.
Hizbollah leader Sheikh Hassan Nasrallah said after Yassin's killing that "the Zionists will discover soon that they have committed a very big folly, to add to their series of previous follies."
Nasrallah said Israel would pay a "heavy price" for its "ugly crime".