JUROUD ARSAL, Lebanon (Reuters) - The barren, rocky hilltops that form Hezbollah’s new front line with jihadists at the Syrian-Lebanese border were tough to capture and supply. Hezbollah commander Hajj Abu Ali says the experience could prove useful in future battles.

A Hezbollah fighter holds his weapon in Juroud Arsal, Syria-Lebanon border, July 25, 2017. REUTERS/Mohamed Azakir

Military jeeps and four-wheel-drive trucks make a slow, bruising progress up newly bulldozed dirt tracks to the mountains near the Lebanese town of Arsal to ferry food and supplies to forces there as fighting rages in the valley below.

“Each battle has its own difficulties,” Abu Ali said, standing on a bombed-out hilltop bunker captured from Nusra Front militants in the area known as Juroud Arsal.

This is the latest front for Hezbollah in its battle with militants to secure Lebanon’s Syrian border, part of the wider role the Iran-backed group has played in support of Syria’s President Bashar al-Assad in the six-year-long war in Syria.

Hezbollah has made rapid advances against Nusra Front since launching the offensive jointly with the Syrian army on Friday, aiming to clear jihadists out of their last border foothold.

Mortar fire pounded targets in the valley and jets struck on the Syrian side of the border during a media trip to the area on Tuesday. Plumes of gray smoke towered into the sky.

“What is tough in some battles is that areas are densely populated, with many civilians. Here you can shell more freely, it’s open and there aren’t many people. But the terrain is the difficult bit - it’s hard to cover ground, and we have to open new roads as we go along,” Abu Ali said.

Since the operation began, Nusra Front has almost been vanquished, Hezbollah says, and the next target is a pocket of territory held by Islamic State militants.

As Hezbollah battles jihadists in this latest offensive, the Lebanese army has adopted a defensive posture guarding the nearby town of Arsal. A big recipient of U.S. and British military support, it has not taken part.

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Hezbollah commanders believe the offensive will soon be over, and say the battle is providing valuable experience. “It could help prepare us for future battles,” Abu Ali said.

But the battle has been hard fought, mainly because of terrain that was long an ideal base for Nusra Front - al Qaeda’s al Qaeda’s former Syria branch and now leader of Islamist alliance, Tahrir al-Sham - as well as for Islamic State militants and other insurgents.

On this particular hilltop, militants had barricaded themselves behind sandbags and dug trenches into the hard stone ground. “It was easy for them to dig in here and shoot at whoever raised their head coming up the hill,” Abu Ali said. Hezbollah had lost fighters that way, he said.

“We dealt with it using artillery and air strikes. We found eight (insurgent) bodies here. Others fled from the area, some on motorbikes.”

A blackened stove, an upturned coffee jar and a shredded green tarpaulin roof cover were the only signs left of the Nusra militants.

EXISTENTIAL BATTLE

Abu Ali said the fight to capture the surrounding hilltops began at dawn on the first day of the operation and lasted 11 hours. Ten Hezbollah fighters were killed, he said.

Security sources say some two dozen Hebollah fighters have been killed overall, and nearly 150 militants.

At a checkpoint further back from the front, Hezbollah fighters urgently waved through an ambulance with blacked out windows returning along the same bumpy dirt track, signposted “to Wadi al-Kheil”, a valley recaptured on Monday.

Tanks, tents and a field clinic sat in the shade of apricot trees nearby.

Hezbollah has lost hundreds of fighters including top commanders in Syria. It says the battle there is an existential one to stop extremists spreading to Lebanon. Its Lebanese critics say it has fueled militant attacks in Lebanon.

A Shi’ite cleric dressed in combat fatigues prayed next to mortar cannon emplacements overlooking the valley on Tuesday.

One fighter was confident of victory soon, and dismissive of the enemy. “See that mountain? That’s where they were the day before yesterday. Now look where they are,” he said, pointing out several kilometers (miles) of ground Hezbollah had taken.

“They are nothing.”