The Lebanese prime minister has called for an immediate ceasefire between Israel and Hezbollah militants, saying his country "has been torn to shreds".
Thousands of Lebanese have fled but many remain trapped
Fouad Siniora said more than 300 people had been killed and 500,000 others displaced in a week of Israeli attacks.
Israel says it carried out 80 air strikes in Lebanon in the early hours of Thursday morning.
And it says its soldiers are now fighting Hezbollah militants along the border just inside Lebanon.
The clashes are taking place north of the Israeli village of Avivim, an Israeli Defence Force spokeswoman said.
On Wednesday evening, Israel said a wave of aircraft dropped 23 tonnes of explosives on a bunker in the south of Beirut where senior Hezbollah figures, possibly including leader Sheikh Hassan Nasrallah, were believed to be hiding.
But Hezbollah issued a statement saying the building targeted was a mosque under construction and "no Hezbollah leaders or personnel were killed in the strike".
Twenty-nine Israelis have died - including 15 civilians killed by rocket attacks - since the Israeli offensive against Hezbollah militants began eight days ago.
On Wednesday, two children were killed in Nazareth by Hezbollah rockets.
FOREIGNERS IN LEBANON
UK: 22,000 (inc. 10,000 with dual nationality)
Figures correct at start of conflict
Wednesday's air strikes from Israel killed more than 60 Lebanese civilians, as two Israeli soldiers and a Hezbollah militant died in clashes.
Barrages of Hezbollah rockets were fired into northern Israel.
Israel launched attacks on Lebanon after Hezbollah captured two Israeli soldiers in a cross-border raid eight days ago.
Many thousands continue to flee Lebanon, and several countries have sent ships and helicopters to move their nationals.
But thousands of others remain trapped, with major roads cut by Israeli bombing, and no supplies reaching many areas.
In other developments:
- Relief agencies say there is a growing need for water, sanitation and medical facilities for those displaced within Lebanon
- French President Jacques Chirac called for humanitarian corridors in Lebanon to protect civilians from Israeli air raids as they flee the fighting
- UN Secretary General Kofi Annan and US Secretary of State Condoleezza Rice are to discuss the crisis on Thursday.
In an emotional televised appeal, the Lebanese prime minister urged the international community to intervene.
"I call upon you all to respond immediately... and provide urgent international humanitarian assistance to our war-stricken country," Mr Siniora said.
"Can the international community stand by while such callous retribution by the state of Israel is inflicted on us?"
He vowed to make Israel pay compensation to Lebanon for the "barbaric destruction".
The Israelis say they are fighting to end the control of Hezbollah over the lives of ordinary people on both sides of the border.
Israeli Prime Minister Ehud Olmert said the campaign against the militants would continue "as long as necessary" to free its captured soldiers and ensure Hezbollah is not a threat.
Israeli Deputy Prime Minister Shimon Peres told the BBC that Israel wanted peace, but could not sit back while Hezbollah fired rockets at Israel.
Wednesday saw further Israeli strikes in the east, south and Beirut, where a Christian district came under fire for the first time.
At least 12 people were killed in a southern village near the city of Tyre and civilian deaths were also reported in other parts of the south and near Baalbek in the east.
The strikes came as Israeli ground troops continued what they call "restricted pinpoint attacks" into southern Lebanon.
Heavy exchanges of fire erupted after Israeli tanks and infantry crossed the border in search of Hezbollah weapons and facilities.
For their part, Hezbollah fired dozens of rockets at Israeli cities including Haifa and Tiberias.