°®Âþµº

The group's use of the opposition's colours and motifs has also brought sceptism from some rebel groups, particularly when another video showed Sarhan with the pre-Baathist tricolour flag upside down.

Daring raid

So when the New Syrian Army reportedly stormed an Islamic State group border crossing in Deir az-Zour province from its base in Jordan last week, many critics were taken by surprise, while others remained sceptical.

Armed with artillery and rifles, the New Syrian Army said it carried out "a daring raid" deep inside IS territory on 3 March. They killed a number of IS fighters close to the Iraqi and Jordanian borders and held their position, in what was probably the first attack of its kind against IS.

"The New Syrian Army is now present in the area of al-Tanf after capturing the border crossing and the areas surrounding it from IS," Sarhan told °®Âþµº.

"First Lieutenant Mahmoud Saleh planned the offensive for one month before the operation was launched. Our reconnaissance units provided us with all the sufficient intelligence to start the military operation," he said. 

The surprise assault began at dawn on 3 March, with a mortar attack on the militants' base. Infantry then stormed the crossing from various points while another battalion provided machine gun and artillery cover, Sarhan said.

"In the early hours of the battle, we managed to take full control of the area of al-Tanf and we raised the flag of the New Syrian Army. IS members were fleeing for their lives, heading towards the checkpoint of Dadad and Alyana," the commander said.

No footage has yet been released showing the force at the border, but Sarhan insisted that, as of Thursday night, the area was still under the New Syrian Army's control and a video would follow shortly.

Videos of the group training and preparing for assaults have been released by the group - but none show them engaged in fighting.

The group also won't reveal the number of its fighters, other than say it is "adequate" and "increasing day-by-day", while a  has shown a number of fighters training.

Armed and dangerous

Sarhan said they receive ammunition and weapons from the international anti-IS coalition, and their stockpiles in videos show rockets, artillery, rifles and vehicles.

The most likely countries backing the force are the US and Jordan, and the commander says they have been working together for over a year.

While it has been suggested that the New Syrian Army is a proxy force for Jordan to secure its borders from IS militants, Sarhan vehemently rejects such a label.

"It is absolutely false and we challenge anyone who claims that we are nothing but a proxy of Jordan to provide compelling proof to back this false claim," he told °®Âþµº.

"These rumours will have no effect upon our will and determination - and we will continue our struggle and efforts until we achieve our main objective, which is the liberation of [Syria's] eastern region."

Sarhan and his fighters' beef with IS is personal, and he - like many in the opposition - view the militants as a counter-revolutionary force who have been allowed to grow by the Assad regime.

Sarhan was one of many Syrians from Deir az-Zour who defected from the army when troops began firing upon protesters in 2011.

Armed, he and his unit protected demonstrators from regime snipers, and the eastern region soon became a stronghold of the Free Syrian Army.

But after a score of major IS victories over the Iraqi army and the capture of heavy weaponry, the FSA were soon forced out of the province as the extremist militants turned their guns on the rebels.

This time its personal

When one Sunni tribe rose up against IS tutelage, they became victims of one of the biggest massacres on Syrian soil - with between 700 and 900 shot, beheaded, crucified or shelled to death.

"We are the sons of the pure tribes who have made a covenant with God that we would not leave our people suffering and being oppressed and just keep watching," said Sarhan.

Many from Deir az-Zour feel their sacrifice has been ignored and the US efforts at degrading IS capabilities have been mostly in Iraq, with money and weapons rolling into Kurdish groups' coffers rather than aiding Syrian rebel militias. 

Since then, Sarhan is said to have survived four assassination attempts by IS militants and still lives under threat of attack.

"The New Syrian Army is about liberating Deir az-Zour in particular from both IS and the Assad-regime, who have been oppressing and committing all kind of brutal crimes against civilians living under their control," the ex-military man said. 

Sarhan insists that the group will not restict itself to commando raids on IS posts, as other FSA units have, but were now taking their first steps to "fully liberating" Deir az-Zour:

"Our coming operations will be a heavy blow to IS. At the same time [the al-Tanf operation] strengthens our determination to liberate more areas from them. We will not depend on 'hit and run' military operations and we will remain resolute and continue our fight against them."

Sarhan is viewed by some as a good candidate for liberating the province. As a popular local man who speaks the language of the street, he is well placed to lead a mass movement against IS from these first steps, it has been suggested.

Syrians in will now be seeing if Sarhan can build on his claims, and become a reactive force to the IS chokehold of the province.

Follow Paul McLoughlin on Twitter: