Israel continued its precision incursion Thursday over the border into Lebanon as the army seeks to destroy the Hizbullah bunkers and lookout posts that have been used to infiltrate Israel.
Israeli artillery cannons thundered and white plumes of smoke rose up from southern Lebanon as Israeli combat engineers and armored vehicles moved against Hizbullah positions.
After Israel's unilateral withdrawal from Lebanon in 2000, the Shiite militia unfurled yellow flags over outposts in sight of Israel's border.
By the end of this round of fighting, Israel wants to ensure that the network of positions that allowed a proxy of Iran to peer over the border and collect intelligence is leveled.
"We need to be in a situation that there won't be any Hizbullah infrastructure near the border," says Reserve Gen. Yakov Amidror, the former head of the Israeli army's planning division. "If we don't take care of it now Hizbullah can return and say they never left."
The general speculated that Israel would have to clear positions six miles north of the border.
Israeli media reported Thursday that Israel's army Chief of Staff Dan Halutz said the offensive against Hizbullah will probably last a long time. And in an apparent attempt to counter the impression that Israel's government is reluctant to launch an invasion of Lebanon, Defense Minister Amir Peretz said there would be no constraints placed on the military.
"If they are hitting us from inside Lebanese territory, we will do everything necessary," he said. "It is entirely clear that we intend to settle the battle decisively.
One security official said Wednesday that a security buffer zone is being created that would "be clean of Hizbullah."
The Israeli army is moving in special forces to clear the area of mines before bringing in bulldozers "to flatten the area and remove any sign of Hizbullah outposts and even trees so that Hizbullah can't enter again," he said.
There is a reluctance in Israel to repeat the sweeping invasion in Lebanon in 1982 because many are concerned about the lack of an exit strategy. But many believe that Israel's achievement so far will be unfinished if there is no significantly stepped-up ground offensive. "We can't only do it from the air, that's too small," said General Amidror.
Deeper into southern Lebanon, Israeli units are believed to be moving against Hizbullah, who have fired more than 1,000 rockets into northern Israel over the past week, according to Israeli media reports.
"This is a minor operation. We are not talking about moving into and cleaning up southern Lebanon," says Shmuel Bar, a Middle East expert at the Herzliya Interdisciplinary Center, a private university outside Tel Aviv.
In Lebanon's south, some 850 foreign nationals and Lebanese UN employees evacuated Tyre Thursday by sea. Their departure came shortly after Israel warned all residents to move north of the Litani River, about 25 miles from the border with Israel.
With Hizbullah showing little sign of breaking, some see Israel's ultimatum as suggesting that its week-long onslaught against south Lebanon, which has claimed at least 300 civilian lives, could indeed strengthen.
"The foreigners have gone and that means the war will really begin now," says Hassan Bazzi, a port worker.
Hundreds of people crammed into vehicles to undertake the perilous trip northward. Normally a city of 100,000, up to 80 percent of residents have left.
Thursday was calmer than previous days. But for Hassan Fawaz, it was the eighth day he had spent trapped with 25 people in a basement near Tibnine, 12 miles south east of Tyre.
"We are very, very scared," says Mr. Fawaz, a translator with the UN peacekeeping force in south Lebanon (UNIFIL), speaking over a cellphone. "The UN says we should stay where we are, but we have been hearing the sounds of bombing 24 hours a day since it began," he says. "We are praying all the time. Pray for us, too."
UN officials estimate that about 60 percent of the population south of the Litani, which swells to about 290,000 in the summer, has already fled north.
Tyre Mayor Abdul Mohsen al-Husseini is struggling to cope with a humanitarian disaster. Some 20,000 people have fled their villages for the relative safety of the city, which has suffered only one air strike so far. "My house was destroyed two days ago," says Akhlas Jaber who had just arrived from Qana. She points to some of her children. "Are these fighters?" she asks angrily. "Is that baby a fighter? None of the fighters are dead, only the women, children, and sheikhs."
Further north, in Beirut, the city was constructing makeshift shelters and people slept in doorways and parks. The number of people who have fled homes has reached 400,000 to 600,000 people, says Asma Andraos of the newly formed governmental Higher Relief Council.
More than 100 public schools have opened their doors, but they are short on supplies. There are few showers or toilets. Most of the inhabitants are women and children who have only what could carry.
"This is the biggest crisis Lebanon has ever faced. When you have a population of 4 million and half a million are displaced, that's a catastrophe," she says.
Most of the displaced come from the south or the devastated southern suburbs of Beirut. Exact numbers are hard to come by. But "it's rising by the day. Thursday 10,000 people turned up at the schools," Mr. Andraos says.
Ali Makki, an IT consultant who volunteers for the Higher Relief Council, said he had fielded heart-breaking calls on Wednesday. One man called asking for food and mattresses because he had taken in two families. "He said, 'I had only $10 in my pocket, and now I don't have anything. But I gave these people somewhere to sleep and I can't ask them to leave,' " says Mr. Makki. He was put on a waiting list at the overwhelmed center.
• Orly Halpern contributed reporting from Haifa, Israel; Lucy Fielder contributed from Beirut, Lebanon; wire material was used in this report.