By Alistair Lyon, Special Correspondent

NAQOURA, Lebanon, July 3 (Reuters) - The threat of attacks like the car bomb that killed six U.N. soldiers in south Lebanon last month is now the greatest obstacle to the peacekeeping mission there, the U.N. force's commander said on Tuesday.

Nearly a year after a 34-day war erupted between Israel and Hezbollah guerrillas, the 13,000-strong UNIFIL force considers it has done a good job in keeping the area calm, alongside Lebanese army troops who deployed in the south after the war.

UNIFIL has faced no hostilities from Hezbollah or Israel since the war ended, but the June 24 bombing that wrecked a Spanish troop carrier has redrawn the security landscape.

"It was an attack against UNIFIL, but broadly speaking an attack against stabilisation in Lebanon," the force's Italian commander, Major-General Claudio Graziano, told Reuters.

"If you really want to destabilise Lebanon, you have to attack UNIFIL," he said in an interview at his seaside headquarters in Naqoura near the Israeli border.

Last year al Qaeda deputy leader Ayman al-Zawahri urged attacks on UNIFIL after it was expanded under U.N. Security Council resolution 1701 that halted the war with Israel.

No group has claimed responsibility for the car bombing, which Graziano described as "quite sophisticated", involving about 50 kg of explosives detonated by remote control.

Hezbollah, a Shi'ite movement with little sympathy for Osama bin Laden's notion of global jihad and no relish for Sunni rivals operating on its southern turf, condemned the attack.

The Beirut government has linked it to fighting in the north where the army has battled a Sunni militant group named Fatah al-Islam at a Palestinian refugee camp for more than six weeks.

Graziano said this might be a logical deduction but he had no firm evidence for it and would await the outcome of separate investigations by the Lebanese government, UNIFIL and Spain.

Asked to identify the greatest challenge to the United Nations Interim Force in Lebanon (UNIFIL), he said: "For sure this terrorist attack and the possibility it can be repeated."

WINNING TRUST

Graziano said new security measures to protect U.N. forces complicated UNIFIL's goal of winning local hearts and minds.

"It's our centre of gravity to keep the cohesion and consent of the people because (resolution) 1701 and peacekeeping is all about support of the population.

"Of course security doesn't accept a discount, but we have to keep very close to the population and in this case explain to them that these security measures are not against them."

UNIFIL's mandate and rules of engagement were robust enough, Graziano said. But the peacekeepers were discussing with the Lebanese army "how to better share and shape the different aspects of force protection" to try to prevent future attacks.

Hezbollah has kept its arms out of sight since the war and has pledged respect for resolution 1701, but it retains a solid presence in the south, where it enjoys widespread support.

Graziano said UNIFIL continued to find arms caches and to hand them over to the Lebanese army, but had not encountered the movement of weaponry or of armed people in the south.

A vital part of UNIFIL's mission, he said, was to "keep a window open" for political and diplomatic developments that could eventually lead to the disarmament of all armed groups.

He said UNIFIL had enough troops to fulfil its mandate and might need to keep similar force levels until such time as the Lebanese army could take over the area independently.

"That means not only having the right capability or the right number of soldiers, but also to have the right trust from the other side (Israel). We are speaking of a period of time that could easily be three years," Graziano declared.

The Italian general said repeated Israeli incursions into Lebanese air space violated resolution 1701 and represented an embarrassment to the Beirut government and the United Nations.

Israel insists the overflights are necessary to monitor alleged weapons smuggling across the Syrian border. It also says they will continue until Hezbollah returns the two soldiers whose capture on July 12 triggered last year's war.

Graziano said UNIFIL could report the reconnaissance flights, but was powerless to halt them. "The only possible solution to convince Israel to stop this is at the highest level," he said, apparently referring to the Security Council.

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