Surveying the rocky no-man's land on Lebanon's eastern border with Syria, Hezbollah fighters recalled the "difficult" battle they fought to recapture much of the terrain from militants.

The Lebanese Shiite movement has waged a five-day offensive across the scraggy landscape known as Jurud Arsal to oust what it says are ex-Al-Qaeda Syrian jihadists.

On Wednesday, Hezbollah brought journalists to its positions overlooking the last pocket of enemy territory.

Despite plumes of black smoke in the distance, fighters appeared relaxed after several days of clashes, grinning in the blistering heat.

"Jurud Arsal's topography is tough and the battle against Al-Nusra Front here was difficult," said a Hezbollah commander, speaking on condition of anonymity. 

"Al-Nusra was entrenched in its hilltops and valleys, turning these areas into combat facilities that even airplanes couldn't reach."

Al-Nusra was Al-Qaeda's Syrian branch before it broke off ties and rebranded as Fateh al-Sham Front last year.

Hezbollah has fought the group in Syria since intervening in support of the Damascus government in 2013.

Jurud Arsal -- a mountainous area around the Lebanese border town of Arsal -- is mostly barren, save for some orchards of cherry and apricot trees that ripened long ago without being picked.

Tens of thousands of Syrian refugees live in and around the town, some in camps.

But security has long been a concern, with Lebanese security forces battling jihadists there in 2014.

On Wednesday, Lebanon's flag had been planted next to the yellow and green flag of Hezbollah in Jurud Arsal.

Around 200 fighters were in a pocket "that does not exceed nine square kilometres," or about three and a half square miles, the Hezbollah commander said.

- Air strikes -

Syrian warplanes have backed the push with regular air strikes from their side of the frontier.

A Syrian army colonel accompanied by Hezbollah fighters could be seen atop a tank Wednesday in the porous border area.

Lebanon's army has not officially declared its participation in the operation but has shelled "terrorists" in the area.

Hezbollah fighters on Wednesday said they had helped protect "the Lebanese army's back".

"We're shouldering the danger for Lebanon -- the danger of explosions and terrorist cells," the commander said. 

Hezbollah's involvement in Syria has intensified pre-existing divides among Lebanese political parties, but the assault in Jurud Arsal has appeared less controversial.

Despite Hezbollah's announcement Monday that the operation was nearly over, the field commander said there was still work to do.

"The battle in Jurud (Arsal) is not over yet," he told journalists. 

"Nusra has an ideology and its fighters are tough. But we too are strong and have an ideology, even if it's a different one."

Extreme Sunni militant groups such as Al-Qaeda consider Shiite Muslims, who make up a majority of Hezbollah's members and supporters, as apostates. 

Since its offensive began, Hezbollah has buried around 20 of its fighters and says around 120 enemy combatants were killed.

Its head Hassan Nasrallah will give a televised address Wednesday, with fighters expecting him to announce the conclusion of the battle's "first phase". 

"Tonight, he will define the course of the fight against Daesh," the commander said, using the Arabic acronym for the Islamic State group.

IS controls swathes of territory in Jurud Arsal and around two neighbouring border towns, the commander said.

"It won't be a difficult task. Its fighters are only a few hundred and spread out in this vast territory."