The security situation in Lebanon is likely to remain "fragile" for the next two or three months, a senior UN envoy has warned.
Lebanon is strewn with the debris of war and the fear of a return remains
Terje Roed-Larsen was speaking on a visit to Jerusalem for talks with the Israeli government.
The UN says an international force is urgently needed to police the 10-day-old truce in Lebanon.
But there have been few substantial offers of troops, and EU officials meet on Wednesday to try to secure pledges.
Some 15,000 Lebanese soldiers are being deployed mainly to southern Lebanon, joining an existing force of some 2,000 UN peacekeepers.
But the ceasefire has been tested by a number of skirmishes and an Israeli commando raid deep inside Lebanon, and Mr Roed-Larsen said the situation remained fragile.
"There is now a security vacuum which the Lebanese government is trying to fill" with the help of international forces, Mr Roed-Larsen told the news agency Reuters in an interview in Jerusalem.
"But I think realistically, up to a point, you will have such a vacuum in Lebanon for the next two, three months," he added.
"The situation is still extremely fragile... Unintended incidents can kick off renewed violence, which might escalate and spin out of control."
Officials from European Union member states are set to meet in Brussels on Wednesday to try to establish which countries are willing to contribute to the force.
And Italy has succeeded in a call for an emergency meeting of EU foreign ministers to be held on Friday.
While Italy has offered troops and leadership of the force, a task that was initially expected to go to France, it has demanded a fresh commitment from Israel to respect the ceasefire.
Israel attracted condemnation from the UN and Lebanon for a commando raid in the Bekaa Valley on Saturday, and since the ceasefire took hold has clashed several times with alleged Hezbollah fighters, resulting in several deaths.
The UN has also expressed concern about Israeli violations of Lebanese airspace.
Israel says such actions are defensive.
On Tuesday, Turkey said it might be willing to contribute soldiers but joined several other nations in expressing concerns about the clarity of the force's mandate - and in particular whether peacekeepers will help disarm Hezbollah guerrillas.
The US has rejected calls for an immediate new UN resolution to lay down more precise terms for the force, with UN envoy John Bolton saying the priority is to get a force on the ground.
Lebanon, meanwhile, continues to be subject to a sea and air blockade imposed by Israel, with the exception of a limited number of flights, including aid and diplomatic missions.
In a meeting with the UN's Mr Roed-Larsen on Tuesday, Israeli Prime Minister Ehud Olmert said the stationing of UN troops along Lebanon's border with Syria to stop the smuggling of arms to Hezbollah would allow it to lift the blockade.
But Syrian President Bashar al-Assad immediately rejected the idea, saying it would be interpreted as a "hostile act".
In Israel, Prime Minister Olmert is facing increasing public pressure to approve an independent investigation into the war despite saying on Monday he would not be party to "self-flagellation".
Senior members of the ruling coalition have backed the call for an investigation, demanded in an open letter signed by hundreds of Israeli reservists.