Tension in Syria between rival rebel groups reached new heights as the US threatened to strike President Bashar al-Assad's regime.

Self-described jihadist groups - some with alleged links to al-Qaeda - say they fear US missile attacks against Syrian military installations would also target them, and that the West was seeking to use moderate rebel factions to keep them in check - much as the US-funded "Awakening Councils" did in Iraq. The result is increasing animosity in Syria between jihadist groups and Western-backed fighters.

The Islamic State of Iraq and Levant (ISIL), an armed group operating in Syria and a US-designated "terrorist organisation", announced last week it would "go to war" against two other rebel groups in the town of al-Bab, in Aleppo governorate.

ISIL's leadership is based in Iraq and its ranks include many non-Syrian fighters. It has declared a "purifying maliciousness" military campaign to round up fighters from the al-Nasr and al-Farouq battalions, both operating under the loose banner of the Western-backed Supreme Military Council.

The two groups had stormed the ISIL headquarters - based in a school - in an attempt to evict its fighters. ISIL had refused to comply with an agreement among the town's rebel factions to stay away from education institutions and allow children to return to school in the new academic year. The raid led to an hours-long firefight, and both sides traded blame after several people were left injured.

The situation in the eastern province of Deir Ezzor, near the Iraqi border, is hardly any better. On Saturday night, deadly clashes in al-Bu Kamal erupted between jihadists and the Allahu Akbar Brigade, an opposition group credited with the capture of the city from Assad forces in November 2012 and which also operates under the Supreme Military Council.

In the northeastern province of al-Raqqa, meanwhile, fighting between ISIL fighters and the Ahfad al-Rasoul battalion, another Supreme Military Council-linked organisation, also killed some 11 people in the past month.

ISIL accused Ahfad al-Rasoul of being collaborators with the Assad regime - and blew up its headquarters, rounding up several of its members. ISIL also released a video that purports to show an Ahfad al-Rasoul commander admitting to being a French intelligence agent.

An Ahfad al-Rasoul fighter told Al Jazeera the confession was filmed under duress, pointing to the commander's shaking voice and tied hands. "Had we been collaborators with the regime, you would not have seen us at the hotspots," said Ibrahim Edliby.

He said ISIL was trying to capture strategic areas from other rebels who had fought for months to take control of territory from Assad forces. "You do not see ISIL fighters in hotspots clashing with the regime. You see them trying to extend their control to areas we struggled hard to liberate."

The Supreme Military Council, promoted by Western and Gulf backers as an umbrella of moderate groups boasting hundreds of thousands of fighters, is being increasingly challenged by thousands of jihadists and foreign fighters, who have flocked to war-torn Syria to fight Assad's regime.

'Enemies of Islam'

Once united in the fight against government forces, the ISIL and other similar groups have recently labelled some Supreme Military Council factions "Sahwat", likening them to US-funded "Awakening Councils" in Iraq. Those armed groups established themselves in Sunni tribal areas in 2005 ostensibly to help the Iraqi government with security, as violence raged throughout the country. The Awakening units were at the forefront of the fight against al-Qaeda and other jihadists in Iraq.

Now, some suspect the US is planning to establish similar armed factions in Syria.

Echoing the fears of jihadist groups that other rebel groups may turn their arms against them - especially if Assad's regime falls - al-Qaeda's leader Ayman al-Zawahiri said in a video recording released on September 11 the "Sahwat the US is trying to create in the Levant will be destroyed - God willing". He urged armed Islamist groups not to "reconcile with secularists and enemies of Islam in any way".

The talk of a possible air strikes by the US on Syrian military installations has accentuated divisions on the ground and deepened the jihadists' suspicions of secular and moderate Islamist armed groups.

The developments in Syria are straying away from US calculations. The Syrian street has never been more attuned with the Islamists and more supportive of an Islamic project in the country the way it is now. Jabhat al-Nusra fighter

Supreme Military Council commanders have unequivocally called on Washington to carry out missile strikes on Assad's military assets, hoping such an offensive could help bring the regime down.

The jihadists, meanwhile, say if the US decides to intervene militarily in the Syria, they themselves would not be spared.

"Once the Syrian skyline is violated, the air strikes would extend to the positions of the jihadists [in rebel-controlled areas]. They will start targeting them in the name of the fight against terrorism," a member of Jabhat al-Nusra, al-Qaeda's branch in Syria, told Al Jazeera..

Bracing for a US attack, members of ISIL have already emptied some of their offices in Aleppo, relocating to more discreet areas in the northern city's suburbs. Commanders in Jabhat al-Nusra have also taken new security measures in anticipation of a US strike, the source in the group told Al Jazeera, speaking on condition of anonymity.

The Jabhat al-Nusra member said he believed the West was intervening in the country because "the US proxies" in Syria were losing ground to the jihadists.

"The developments in Syria are straying away from the US calculations," he said. "The Syrian street has never been more attuned with the Islamists and more supportive of an Islamic project in the country the way it is now. Syrians have been rejecting the Western-backed projects in the country, including the Jarba project."

The Jarba project is a proposal put forward by Ahmad Jarba, the leader of the opposition Syrian National Coalition. He called for the creation of a 6,000-strong national army to unite the hundreds of rebel groups and to counter the influence of the jihadists.

The proposal has not yet materialised because of a lack of logistical and financial resources, said spokesman Louay Mokdad of the Supreme Military Council, the military wing of the Syrian National Coalition.

"It would be a proper national army with the purpose to protect the Syrian people from those who kill them, be it the Syrian regime or anyone else," Mokdad told Al Jazeera. "If the jihadists see themselves in a position where they are killing Syrian people, then this would be their problem."

'ISIL doesn't represent me'

Aaron Zelin of the Washington Institute, whose research focuses on jihadist groups and networks, said he did not believe there was an Iraqi-like Sahwa movement brewing against Syria's jihadists.

The jihadists in Syria had learned from the mistakes of Iraq's jihadists a decade ago, he said. Those who operated in Iraq "used excessive violence, targeted Sunni Muslims and tried to institute a narrow interpretation of Sharia".

Meanwhile, jihadist groups in Syria, especially Jabhat al-Nusra, have developed a measure of popular support among residents in areas under their control by providing social services. They are seen as fair and honest, especially when other groups resorted to looting and banditry.

"We have seen them doing some sort of governance and outreach to people there, and therefore they have been able to show people they aren't these scary monsters," said Zelin.

But tension still exists between residents and jihadi groups, and this has reportedly heightened in recent weeks. Several activists have been threatened and imprisoned for criticising the Islamists and the public executions of Assad loyalists. The arrest of a local journalist by ISIL in Aleppo on Saturday spawned an "ISIL doesn't represent me" campaign on Twitter [Arabic].

But Zelin said protests against jihadists have been limited.

As for fighters under the direction of the Supreme Military Council, they "cannot afford to turn against jihadist groups", he said.

"The fighting forces on the battlefield are interconnected and continue to fight [Assad's regime] together. The jihadists are fighting with the more mainstream Islamists, as well as non-Islamists," Zelin told Al Jazeera.

"This is because there is no such group that is qualitatively stronger than the others and, therefore, they need to work together to survive."

Follow Basma Atassi on Twitter: @Basma_