BEIRUT: The impact of the stunning seizure of large tracts of northern Iraq by the extremist Islamic State of Iraq and Greater Syria (ISIS) last week could have significant consequences for the Syrian regime’s ability to hold onto power.

Already the reverberations of ISIS’ dramatic advance toward Baghdad is being felt in Syria, with Syrian rebels in the Qalamoun area taking advantage of the return home of Iraqi Shiite paramilitary forces to stage a counterattack in Rankous.

“The rebels launched a surprise attack on the edge of Rankous. The fighting is ongoing,” a veteran Hezbollah combatant said Saturday, adding that the party had lost 11 fighters in the clashes.

Despite a series of battlefield successes in western Syria over the past year, the Assad regime barely has sufficient forces to hold its newly seized territory let alone retake the entire country.

With the Syrian army decimated by desertions and exhaustion, the regime relies heavily on its allies, chiefly Hezbollah as well as Iraqi paramilitaries. It is estimated that there are around 5,000 Hezbollah fighters in Syria at any one time and the party represents the main offensive force in launching operations backed by Syrian airpower and artillery to recapture territory. There were an estimated 20,000 to 30,000 Iraqi Shiite fighters serving in Syria before the ISIS offensive in northern Iraq. According to diplomatic sources, the Iraqis were being offered six-month contracts by Iran to serve in Syria with a guaranteed job on their return home.

“They are picking up all the unemployed Shiites,” a European diplomat in Beirut said.

Iran also helped establish the National Defense Force, a mainly Alawite militia that is thought to number around 80,000 fighters. The main role of the Iraqi Shiites and the NDF is to garrison captured territory, allowing Hezbollah and the Syrian army to mount fresh offensives elsewhere.

Rankous fell to the Assad regime in April during the Hezbollah-led campaign to seize the Qalamoun district. Afterward, Hezbollah was deployed elsewhere and the town was garrisoned by the Iraqi groups and the NDF. But the advance of ISIS from northern Iraq toward Baghdad and a vow by Abu Mohammad al-Adnani, the group’s spokesman, to take the war to the “filth-ridden city” of Karbala and Najaf, “the city of polytheism,” has given the Iraqi Shiites in Syria a more pressing commitment than defending Syrian territory.

The Iraqi government has authorized the arming of Iraqi volunteers to meet the ISIS challenge. The mobilization effort was augmented by a fatwa issued last week by Grand Ayatollah Ali Sistani, Iraq’s most senior Shiite preacher, who called on Iraqis to “fight terrorists.”

Thousands of Iraqi Shiites reportedly have heeded the call and are flocking to recruitment centers. It is unclear how many Iraq paramilitaries have been recalled from Syria (although some were being sent back home even before last week’s ISIS campaign), but their combat experience could prove useful if the ISIS advance reaches Baghdad or even areas further south.

Much depends on developments in coming days. The Iraqi army Saturday regained two towns from ISIS in what appeared to be the start of a pushback. On the other hand, diplomatic sources say they have information that senior Iraqi government officials have sent their families to Amman in Jordan, suggesting the prospect of a panicked collapse similar to the rout which allowed ISIS to seize Mosul last week.

Furthermore, although ISIS is leading the offensive toward Baghdad, large numbers of Sunni Iraqis, including ex-Baathists, have reportedly joined the advance, not in support of the extremist group but motivated by anger toward Prime Minister Nouri al-Maliki’s government.

The ISIS campaign, therefore, appears to be morphing into a full-blown Sunni uprising which is a far greater threat to the Maliki government and Iraq’s territorial integrity than an audacious advance on Baghdad by a few thousand ISIS militants.

That leaves Assad and his Iranian allies in a quandary. If a significant number of Iraqi Shiites are redeployed from Syria to Iraq, then it is likely that rebel groups will take advantage of the weakened loyalist forces to try and roll back some of the regime’s territorial gains. Indeed, analysts had been anticipating a resumption of rebel activity in the Qalamoun area even prior to the latest crisis in Iraq. The mountainous Qalamoun, which runs into Lebanese territory, presents difficult terrain to dominate and defend against lightly armed insurgents. The Damascus-Homs highway has returned to the status prior to the regime’s offensive against Qalamoun in November with loyalist forces controlling it during the day while it has become too dangerous to drive along at night.

According to the veteran Hezbollah fighter, the party’s leadership has decided to mount an operation to rid the eastern mountain chain of rebel fighters once and for all. Security sources estimate there are 3,000 Syrian fighters holed up in the mountains between Tufail and Ras Baalbek.

“It’s impossible for us to control all the mountains along the border, but we have enough people to do reconnaissance and ambushes,” the Hezbollah fighter said.

If Hezbollah is obliged to fill the gap left by the departing Iraqi paramilitaries, it will place further burden on the party’s community of supporters. When Shiite areas of Lebanon were being suicide car bombed by ISIS and other Sunni jihadist radicals earlier this year, there was general unanimity within Hezbollah’s support base at the necessity of the party’s combat role in Syria. But the last car bomb attack occurred two and a half months ago and since then Lebanon has enjoyed some relative stability.

Now, there is a sense of unhappiness building among the families of Hezbollah fighters who are beginning to question in larger numbers how much longer their fathers, husbands, brothers and sons will be sent to the Syrian front.