Last week, deadly clashes erupted in the northern Syrian town of Azaz between a powerful jihadist rebel group linked to al-Qaeda, the Islamic State of Iraq and the Levant (ISIS), and forces affiliated with the Western-backed Free Syrian Army (FSA).
Although the fighting might appear to be evidence of the increasing fragmentation of the armed opposition to President Bashar al-Assad, for many observers it is the first clear sign of a backlash against al-Qaeda's presence in Syria.
Evidence of this rejection began to emerge soon after Isis was formed in April.
The group - consisting mostly of foreign fighters - was initially presented as a merger between the Islamic State of Iraq (ISIS), a militant umbrella group that includes al-Qaeda in Iraq (AQI), and a Syrian jihadist rebel group, al-Nusra Front.
However, the announcement was swiftly rejected by the leader of al-Nusra Front, Abu Mohammed al-Jolani, who refused to follow the orders of AQI leader Abu Bakr al-Baghdadi or al-Qaeda's overall leader, Ayman al-Zawahiri.
Since then the two groups have retained their separate identities and the ideological split between them has grown increasingly obvious.
Rebels v rebels
The clashes in Azaz have not been the first between Isis and FSA fighters.
When FSA brigades and Alwiya Ahfad al-Rasoul (an independent Islamist group believed to be backed by Qatar) took the northern city of Raqqa, they soon came under attack from Isis fighters, who eventually seized control.
There has also been fighting between al-Nusra Front and Isis over oilfields in the north-eastern province of Hassakeh.
Many civilians, activists and journalists have also been detained by Isis, and the group is accused of responsibility for many of the atrocities carried out by rebel forces during the conflict.
"Isis has a clear sectarian agenda," says Mezar, an activist in Raqqa.
"They kill and slaughter anyone who is not like them. They definitely do not represent our revolution, but they are damaging its image and values."
The fragmentation of the armed opposition has contributed to the lawlessness in vast areas of Syria that are not under the government's control.
A recent study published by IHS Jane's analyst Charles Lister estimates that there are as many as 1,000 rebel groups, who between them have 100,000 fighters.
There are about 10,000 jihadists fighting for Isis and al-Nusra Front, and another 30,000 to 35,000 hardline Islamists who are focused on Syria rather than global jihad, he says.
A further 30,000 to 40,000 fighters belong to groups with a more moderate Islamist character.
Mr Lister concludes that the core of the Syrian insurgency is composed of Islamist groups of one kind or another, and warns that it should not necessarily be interpreted as a concerning development.
However, Western powers backing the opposition have clearly been troubled by the growing power of jihadists and hardline Islamists.
In the past year, they have made an effort to restrict their support to moderate Islamist and secular groups with nationalist agendas.
In November 2012, a meeting was convened in Turkey to help build momentum among groups that oppose sectarianism.
Representatives of almost all battalions and brigades participated, except al-Nusra Front and Liwa Ahrar al-Sham, a powerful group that later formed the Syrian Islamic Front (SIF).
The meeting resulted in the creation of the Supreme Military Council (SMC) and a General Staff of the Free Syrian Army, headed by Gen Salim Idris.
The map of Syria was also divided into five different fronts, each governed by a military council that co-ordinates the various groups on the ground. Operations rooms for each front were set up in Turkey or areas under rebel control.
It is very difficult to ascertain exactly how many fighters are affiliated to the SMC, particularly as smaller groups have been known to shift allegiance depending on who can provide the most funding and ammunition.
There is scepticism about the influence of Gen Idris and the SMC, and the extent of their control over events on the ground.
It has even proved difficult to say with certainty whether particular groups are secular or Islamist. Some nationalist groups have appeared in battles, including the Kataib al-Wihda al-Watania (National Unity Brigades) in Idlib province.
Many rebels have said they or their groups have been forced to adopt Islamist names, slogans and imagery to ensure they get funding.
"Many of the fighters in the most hardline brigades don't even pray, but they have to say Allahu Akbar (God is great) on camera so they get money," Ahmed, a citizen journalist in Idlib province, said.