A rocket was fired from south Lebanon towards Israel on Sunday, Lebanese security sources said. Residents of the northern Israeli town of Metula reported hearing a blast.

"An explosion was heard. Soldiers are searching the area. The cause is still being investigated," a spokeswoman for the Israel Defense Forces said. A second Israeli military source told Reuters the explosion was probably caused by a mortar.

Israel Defense Forces troops were still searching for rocket fragments as of Monday morning.

The incident came amid heightened tensions in the region over Syria's civil war. Damascus has said it will respond to Israeli air strikes that reportedly targeted suspected Iranian missiles in Syria destined for the Lebanese militant group Hezbollah.

The rocket launch could be heard from the Lebanese town of Marjayoun, about 10 km (six miles) from the Israeli border, residents in the Lebanese town said.

Earlier on Sunday, two rockets were fired into a Shi'ite district of southern Beirut after Hezbollah leader Hassan Nasrallah pledged his Shi'ite Muslim guerrilla group would fight in Syria until victory for President Bashar Assad.

Assad is battling a two-year rebellion in which the United Nations says at least 80,000 people have been killed.