Israel's widening military offensive brought to at least 50 the number of Lebanese civilians killed since Wednesday - when Israel attacked Lebanon to rescue two Israeli soldiers captured by Hezbollah fighters - said Lebanese security officials talking on conditions of anonymity because they are not authorised to speak to the media.
Residents of southern Beirut heard the impact of at least four Israeli missiles early on Friday and the Lebanese army responded with anti-aircraft fire.
Hezbollah's Al-Manar TV and other local stations said a bridge in the area was hit. Security sources said the main highway to the airport and the south was also hit.
Sheikh Hassan Nasrallah, the Hezbollah leader, has his office and residence in the district of Haret Hreik in south Beirut. Hezbollah's Shura Council - its decision-making body - and their TV station are also nearby.
Israeli jets dropped leaflets on Thursday warning people to stay away from Hezbollah offices.
Police said a fuel storage tank at a power station on the coast was destroyed during the strikes.
Hezbollah targets on the outskirts of Hermel, near the border with Syria, were also hit by Israeli planes, police said.
The Israeli army said Hezbollah fighters fired more than 100 rockets on northern Israel on Thursday, killing two people, wounding 92 others and hitting Israel's third largest city, Haifa.
A couple run past a bombed bridge
after Israeli air strikes on Friday
Hezbollah, a Shia group backed by Iran and Syria, denied it had fired on the port city.
Israel tightened its blockade of Lebanon by carrying out seven air raids over a 20km stretch of the highway between Beirut and Damascus, the Syrian capital.
The road was closed as a precautionary measure, the authorities said.
The road across the border from Syria was the only major entry point into Lebanon still operating after Israel blockaded ports and destroyed the runways at Beirut's airport on Thursday.
Israeli jets destroyed fuel tanks
and a runway at the airport
A senior Israeli officer said the blockade would be maintained throughout what he said would be a prolonged offensive against the Lebanese resistance group Hezbollah.
At least 50 civilians have died in Israeli raids since Hezbollah captured two Israeli soldiers in a cross-border raid on Wednesday.
Ehud Olmert, the Israeli prime minister, ordered the army to continue with operations in Lebanon after meeting his defence minister and army chief of staff.
"The government has authorised the army to press on with its operation in Lebanon and hit more targets," a government official said.
The violence is the fiercest since 1996 when Israeli troops still occupied part of south Lebanon.