Security sources say Israeli warplanes have attacked targets in a Hezbollah stronghold just south of the Lebanese capital, Beirut.
News reports say a bridge and a fuel storage facility at an electric power station were hit early on Friday. At least three airstrikes were heard as Israeli jets flew overhead. There were reports of anti-aircraft fire.
Hezbollah's headquarters are in the area. There was no immediate word on casualties.
Earlier, Lebanese security sources say Israeli warplanes struck the highway linking Beirut to the Syrian capital, Damascus.
Iranian President Mahmoud Ahmadinejad said any Israeli attack against Syria would be considered an attack against the whole Islamic world and would bring a fierce response. Iranian state media quoted Mr. Ahmadinejad as making his remarks in a telephone conversation with Syrian President Bashar Assad.
Israel has intensified its attacks on Lebanon in an unrelenting military campaign that was launched after Hezbollah guerrillas kidnapped two Israeli soldiers Wednesday.
On Thursday, Israel carried out attacks deep inside Lebanon -- striking Beirut's international airport for the second time and pounding Lebanese army airbases near the Syrian border. The Israelis also a imposed a sea and air blockade on Lebanon.
Lebanese officials say more than 50 people have been killed in Israeli attacks. Israel says eight of its soldiers have died in the fighting thus far.
Hezbollah launched scores of rockets Thursday into northern Israel, killing at least one person. More than 90 Israelis have been injured.
Israeli officials said a Hezbollah rocket attack hit Israel's third-largest city, Haifa, but there are no reports of injuries. It was the first time the rockets have hit as far south as Haifa, some 50 kilometers from the Lebanese border. Hezbollah denied responsibility. Israel's ambassador to the United States, Daniel Ayalon called the strike on Haifa a "major, major escalation."
This is Israel's largest incursion into Lebanon since it withdrew from that country six years ago.