NABATIYEH, Lebanon (Reuters) - Israeli warplanes fired rockets at suspected Iranian-backed Hizbollah positions in south Lebanon on Thursday, a security source said. The source said two Israeli planes fired a total of four rockets at the Iqlim al-Toufah ridges just north of the Israeli south Lebanon occupation zone. There was no immediate report of casualties. Israel has launched 61 air raids on Lebanon since the beginning of 1998. The security source said there was an exchange of shelling overnight, with several shells hitting villages close to the occupation zone. The Israeli air raid came hours after Hizbollah (Party of God) guerrillas killed a pro-Israeli South Lebanon Army (SLA) militia officer by shelling his position in the western sector of the zone. The Moslem guerrillas are fighting to oust Israeli forces and their SLA local militia allies from the 15-km (nine-mile) deep south Lebanon zone.