ARSAL, Lebanon — Syrian rebels and their Lebanese allies currently in command of a crucial corridor that links rebel havens in Lebanon with the embattled Syrian capital of Damascus are preparing for a massive government offensive aimed at bringing the strategic area back under government control.

Rebels and activists in the Lebanese border town of Arsal say they expect the offensive to attempt to cut off sympathetic areas in Lebanon’s Bekaa Valley from rebel-controlled villages just across the border in Syria.

The enclave that has sprung up on both sides of the border near the Jebel Qalamoun mountain peak represents the largest rebel haven near Damascus, the ultimate goal of the insurgents. Its population is swollen by Syrian refugees and fighters who fled the government offensive earlier this year that retook the cities of Qusayr and Homs. Now tens of thousands of rebel fighters are preparing to make a final stand to keep Arsal from being cut off from the Syrian battlefield.

“We will fight to the last man,” said Abu Omar Hujieri, a Lebanese activist and fighter who has ties to most of the rebel factions in the area. With Qusayr and Homs essentially back under the control of the government of President Bashar Assad, a government success in seizing the Jebel Qalamoun region would finish the rebel presence here.

Almost from the beginning of the anti-Assad uprising 30 months ago, Arsal has been a crucial logistics hub and haven for Syrian rebels, who found the mostly Sunni Muslim population, with its strong family and political ties to Syrian Muslims, ready to openly assist.

“This is our war just like theirs,” Abu Omar explained of the Lebanese involvement. “They are our family, our neighbors and our friends. All the people of Arsal are with the rebellion.”

With about 30,000 refugees joining the 40,000 people who already lived here, the two communities appear to be acting as one even as the rest of Lebanon struggles to absorb, politically and economically, more than a million refugees from both sides of the conflict. Signs of rebel sympathy abound, and the town has made housing available to tens of thousands in Arsal and the surrounding villages.

The situation is alarming to Hezbollah, the Shiite Muslim group that’s Lebanon’s most powerful political organization and a staunch ally of Assad’s. Hezbollah officials say the tens of thousands of rebel fighters in Arsal and on the Syrian side of the border nearby leave Lebanon vulnerable to terrorist attacks.

A Hezbollah commander, speaking only on the condition of anonymity because he wasn’t allowed to discuss sensitive matters with a reporter, said dangerous traffic moved both ways across the border, not just from Arsal into Syria but also from rebel-held Syrian cities such as Yabrud into Lebanon.

“The terrorists prepare booby-trapped cars in Yabrud and then they enter Lebanon through the smuggler routes to Arsal,” the commander said.

Hezbollah is expected to commit scores of its fighting units to the battle in this area, and it’s been conducting reconnaissance missions on both sides of the border to plan an offensive, an undertaking that’s complicated by the area’s rugged mountains, which sit barren of trees year-round but fill with heavy snow in the winter.

“Hezbollah has been training some special forces units to fight in this area,” the commander said. “It is different to fight in those mountains than the cities” or in southern Lebanon, where the group traditionally operates.

That snowfall is what has both sides anxiously watching the calendar and the weather as winter draws near. Snow will make fighting with heavy weapons nearly impossible.

“We estimated there was a one-month-long opportunity to do this after the Eid holiday,” which ended last week, the commander said. “And now there’s less time.”

That’s because the Syrian army hasn’t yet completed its operations to seize control of the Ghouta area east of Damascus. Retaking Ghouta was considered a prerequisite to moving on to the Jebel Qalamoun area, the commander said.

Seizing Ghouta, where the Assad regime was accused of using chemical weapons in August, would, along with clearing the Jebel Qalamoun area, break the rebel siege of the capital. The slow progress of that effort might force the regime to delay an offensive into Jebel Qalamoun until spring, according to reports in pro-Syrian regime news outlets.

A delay would certainly suit the rebels, who claim to have turned Yabrud into a workshop to produce mortars and other weapons they hope will help keep the area in rebel hands.

As has happened elsewhere, the rebel forces in the Arsal-Qalamoun area have undergone a radicalization in recent months, with the Western-backed Free Syrian Army largely collapsing as rebel units have joined more radical Islamist-led groups. The Farouk Brigade, the secular fighting group that was once dominant here, has begun to splinter, and control is now in the hands of Jaysh Islam, a coalition of Islamist units from the Damascus area led by Liwa al-Islam, perhaps the most militarily effective purely Syrian group in the country.

“We have no problem coordinating our rebel activities with Islamists,” said a young rebel fighter here who called himself “Salem” and who wore the same long beard and flowing hairstyle that’s common among devout rebels. “The Farouk, Nusra, Liwa Islam, these are all Syrian rebel units that work together and will fight and die together to protect Qalamoun.”

“Nusra” referred to the Nusra Front, an al-Qaida-aligned fighting group that the United States has designated a terrorist organization.

“Nusra is full of people that we know. They’re Syrian, and we will always work with them,” said another rebel, who called himself “Ahmed.”

As he and Salem smoked cigarettes in a small refugee enclave next to a mosque that’s rumored to be affiliated with Nusra, he explained the difference between that al-Qaida affiliate and the Islamic State of Iraq and Sham, another al-Qaida group that has recently seized control of many of the key border crossings with Turkey from the secular Free Syrian Army.

“We Syrians are a moderate people who want a society that respects all minorities and religions,” Ahmed said. “These groups are part of our community and reflect an Islamic view that is also Syrian. So we trust them and want them in this revolution. (The Islamic State of Iraq and Sham) has many foreigners. We don’t know them and we don’t know what they want. Right now they are helping us, but if that changes … “

His comment made the other men in the room murmur with concern. Nobody wanted to finish the thought that this revolution, as bloody as it’s already been, with more than 100,000 dead on both sides, might turn to further violence even if the rebels win.

“But if we lose Qalamoun, we will be finished,” Salem added. “We have to fight to the end there, because if we lose, we’ll have to sit in this room forever.”

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