An Israeli air raid hit a crowded area in Beirut's southern suburb, destroying a residential building, killing at least 15 people and wounding 24 on Monday.
Police said Israeli rockets hit the Shiyyah neighbourhood that had been spared so far.
Hezbollah's stronghold of Haret Hreik nearby had been levelled by air raids over the past four weeks.
Rescue workers were trying to clear the rubble of the destroyed building to look for possible casualties, witnesses said. Other buildings were also badly damaged.
Israeli aircraft pounded southern suburbs of Beirut as dawn broke.
The fighter-bombers carried out five raids in less than an hour, attacking with bombs and air-to-ground missiles.
One civilian was killed and seven wounded in Israeli strikes on the village of Shmistar in the eastern Baalbek region, a security source said.
In a separate strike on the Baalbek region, 10 people were killed and 23 wounded in the nearby Brital village, officials from the Lebanese civil defence said.
Earlier, about 30 Israeli commandos landed by helicopter on a hill overlooking Ras al-Biyada, south of Tyre, raiding an apartment before clashing with Hezbollah fighters, Lebanese security officials said.
UN troops said Tyre had been cut
off by Israeli air raids
At least five Lebanese - including a soldier at a nearby checkpoint - were killed in the raid, officials said. The Israeli military reported eight soldiers wounded, two seriously.
Seven members of one family were killed in an Israeli air strike on a house in the village of Ghazzaniyeh in the south of Lebanon, police said.
Four people were killed and 14 people wounded in a similar strike in Kfar Tibneet village.
Fourteen more civilians died when an Israeli bombardment struck buildings in Ghaziyeh, close to Sidon, according to police who said their corpses were extracted from the rubble.
Israeli jets also staged raids in the nearby village of Haruf as well as the town of Nabatiyeh where one woman and her son were killed.
Hezbollah's television station, Al-Manar, said the group had engaged Israeli infantrymen attempting to advance on the border villages in south Lebanon.
The Israeli military said three of its soldiers were killed in the clashes which centred around the town of Bint Jbeil.
Two soldiers died after being hit by an anti-tank missile, while a few hours later a third soldier died by sniper fire in the same area.
The deaths brought to 61 the number of Israeli soldiers killed since July 12.
The port city of Tyre has been completely cut off from the rest of the country by Israeli bombardments, witnesses and police said.
A Red Cross worker tends to one
of Monday's injured
A makeshift bridge in Qasimiya, north of Tyre, and the road leading out of the city to the south, were both bombed.
UN force spokesman Milos Strugar said "the provisional bridge north of Tyre, over the Litani river, and which connects the city to Sidon, has been cut".
The temporary bridge had been built after Israeli warplanes destroyed two other bridges two weeks ago.
Two Israeli raids targeted the road leading to the Masnaa border post, knocked out by previous attacks and hit again each time residents filled in the craters so as to be able to drive around, Lebanese police said.
Five civilians were killed when Israeli jets launched two successive raids on three buildings in the city, causing them to collapse.
The apartment buildings were situated next to the target of an Israeli naval commando operation last week.
A driver was killed when eight Israeli raids struck villages in the southern part of the Bekaa valley, police said.
Also on Monday, Fuad Siniora, the Lebanese prime minister, said that only one person died in an Israeli air strike on the border village of Houla, correcting his earlier claim that dozens of people had died.
However, a UN spokesman said late on Monday that the toll in Houla had risen to five.
Siniora shed tears as he spoke
about the deaths in Houla
During a meeting of Arab League foreign ministers earlier in the day, Siniora shed tears when he said 40 people were killed in Houla.
However, he later said: "It turned out there was one person killed. They thought that the whole building smashed on the heads of 40 people. Thanks to God they have been saved.
"Those who really shoot to kill innocent people prove that they have the intentions to kill and the intention is quite criminal enough. Nevertheless they are not killed. They are safe."
Israeli soldiers had been fighting Hezbollah close to the border village early on Monday.
Israel also said on Monday it had decided to withdraw its ambassador to Venezuela over Hugo Chavez's opposition to its offensive against Hezbollah in southern Lebanon.