By Paul Reynolds
World Affairs correspondent, BBC News website
Israel is mobilising army reservists
Israel appears to be preparing to extend its ground operations in southern Lebanon to set up some kind of buffer zone, recalling its invasion of 1978 which took it up to the Litani River some 20 km to the north.
Its need to put in ground forces shows the limitations of air power. Air strikes have been used, in a version of the tactics developed by the US air force in the two Gulf wars, to pound Hezbollah targets in Beirut and closer to Syria - source of Hezbollah's arsenal, according to the Israelis.
The aim has been to hit missiles, firing and storage sites and transport links. The effect has also been to cause civilian casualties and huge damage.
Now warnings are being given to those civilians left in Southern Lebanon to get out, though how they can do so easily and quickly along blown up roads is unclear.
And Human Rights Watch has urged Israel to allow civilians safe passage. Its Middle East director Sarah Leah Whitson said: "Israel should warn people of attacks, but those warnings can't be used
to justify harming civilians who remain. Civilians who can't evacuate are still fully protected by international law."
Aims not fulfilled
The prospect of major ground incursions indicates that Israel is some way off its stated aim of trying to destroy Hezbollah's capability.
Nine days after its operations began, it is still fighting just inside Lebanon within sight of its northern border.
On Thursday four soldiers were killed by Hezbollah in an ambush there.
Brigadier-General Alon Friedman told the Israeli paper Maariv: "It's possible that in the coming days our ground operations will increase."
It looks therefore that this conflict will go onto well into next week.
It is worth knowing something about the ground in Southern Lebanon. This helps explain why infantry troops are invaluable.
Israeli ground troops are pushing further into Lebanon
It is very mountainous and the rock has allowed the formation of innumerable caves in which Hezbollah fighters (and before them Palestinians) can hide.
The irregular terrain is ideal guerrilla country and not easily traversed by Israeli tanks and other armoured forces.
So troops have to get out and fight, which leaves them vulnerable to the firepower and local knowledge of the Lebanese guerrillas. Israel has already taken casualties in the limited fighting that has taken place already.
Because of the delay in Israel entering southern Lebanon, Hezbollah forces have had a chance to regroup and re-infiltrate the area to set up positions.
Its main strength might be in missiles but it has fighters as well and their moment might have come. In the meantime, it has presumably moved some of its rockets back and has held others in reserve that could be fired over the top of any buffer zone.
It is also not impossible that elements of the Lebanese army might resist an Israeli invasion, though its forces in the south are extremely limited, only a few hundred.
It is difficult to see how Israel can fulfil its intentions without entering southern Lebanon in some force and some observers had been expecting such a movement before now.
The Litani operation
In 1978, 25,000 Israeli troops moved rapidly about ten kilometres into Lebanon before going onto the Litani River.
Their aim in that invasion was to remove fighters from the PLO. They later largely withdrew their troops and set up a buffer zone (they called it a security zone) and encouraged a local Christian militia to police it.
The plan ended in failure and the Israelis withdrew in 2000, hoping that the Lebanese army would deploy but fearing, as happened, that Hezbollah would take over.
In 1982, Israel went all the way to Beirut.
The obvious question therefore, if it goes for a buffer zone, is - how long will it stay? It is easy enough for the Israelis to get in - they seem prepared to accept losses in this effort - but how quickly would they leave?
They say they do not want to stay but intentions and deeds do not always coincide.
That brings in the diplomacy, which has been ineffective so far.
The Americans are supporting the Israeli demand that there can be no return to the status quo under which Hezbollah watchtowers were overlooking Israel.
That means no ceasefire without a radical shift in the balance of power and influence first. And that means more Israeli attacks.
The US Secretary of State Condoleezza Rice is expected in the region next week, so the ball is beginning to roll, though only slowly.