Irbid: The Free Syrian Army commander, head of a moderate rebel force fighting just across the border in southern Syria, watched helplessly for months as better-funded Islamist militant groups peeled off half the 2,000 fighters from his brigade.

That changed in February when an intelligence operative from a country he refuses to name handed him an envelope full of cash — salaries for his remaining combatants.

“It’s a good amount of money; I can keep my fighters,” the commander said, as scented smoke from his arghileh [water pipe] obscured a scar across his face, the product of a battle in Syria, just 16 miles north of this drab Jordanian town.

In recent months, Syria’s so-called “southern front” has become the focus of a reinvigorated US-backed initiative to bolster faltering opposition forces now losing ground in their three-year battle to overthrow Syrian President Bashar Al Assad.

With peace talks stalled and a pronounced slide toward Islamist militancy in the rebel ranks elsewhere across Syria, Washington and allied foreign governments are increasingly concentrating on helping insurgents based in southern Syria. Northern Jordan has become the staging ground.

It is here that US officials and their Arabian Gulf allies, notably Saudi Arabia, are recalibrating their approach in what many view as a last chance to turn around the civil war that has begun to tilt heavily in favour of Assad. But such a strategy could prove too little too late, the type of intra-rebel clashes that have come to define the opposition in northern and eastern Syria has already begun to wreak havoc in the south.

The foreign powers are hoping to re-energise what remains of the US-backed Free Syrian Army as a “moderate” alternative to extremists with such groups as the Al Qaida-affiliated Al Nusra Front — deemed a terrorist organisation by Washington — that seek to impose militant Islamic rule.

The cash-stuffed envelopes meant to secure the loyalty of rebel fighters are an essential component of the embryonic southern campaign, according to interviews in Jordan with opposition commanders. All insisted on anonymity because they were not authorised to speak about operational matters.

“Every rebel and activist is looking to the much-vaunted southern front for good news and restored hope,” said Joshua Landis, director of the Centre for Middle East Studies at the University of Oklahoma.

Opposition strategists have long viewed the south as a potential backdoor means of attacking Damascus, the Syrian capital, only 110 kilometres from the Jordan border. The area is also close to Israel, which, like Jordan, is alarmed about a growing extremist presence on its frontier.

But the revamped strategy also appears to have as much to do with counterterrorism — battling the rise of Islamic militants — as ousting Al Assad.

West-backed rebel commanders have accused Al Nusra forces of launching a wave of assassinations and kidnappings against Free Syrian Army rivals in southern Syria. Last week, according to rebels here, Al Nusra fighters kidnapped and executed a low-level battalion leader, Fadi Qarqamas, whom they accused of colluding with the government.

The killing prompted FSA commanders to convene to decide whether they would now be forced to fight Nusra as well as the Al Assad government. The Islamic State of Iraq and Syria, the ultra-fundamentalist Al Qaida spin-off group that holds sway elsewhere in Syria, is largely absent in the south.

“We are now convinced that [Al] Nusra Front in the south is like Isis in the north,” one commander said, noting how the Islamic State faction has shifted its focus to dominating rival rebel brigades.

Though cash has begun to flow, southern commanders say they have yet to witness a significant influx of armaments, especially the portable anti-aircraft missiles that rebels in the north have long sought to counter Syrian government air power. US officials fear that such weaponry could fall into the hands of Islamist militants, who could target civilian airliners.

“We think weapons supplies are imminent,” one FSA commander said, “but so far nothing has come through.”

Irbid, traditionally a major crossing point for Syrian-made textiles and foodstuffs, has been transformed into a rebel staging hub and rest area along the more than 300-km border.

Southern rebel commanders have aggressively marketed themselves to potential Western patrons as the “moderate” variant favoured by Washington. That is so despite the increasingly heavy presence of Al Nusra Front guerrillas and Jordanian insurgents, including followers of Abu Musab Al Zarqawi, the late Al Qaida icon and Jordanian national long a scourge of US forces in Iraq.

“The idea is that the southern front must have a moderate point of view, not extremist,” another battalion commander said.