The al-Qaeda-styled group in Syria is Jabhat al-Nusra li-Ahl al-Sham (the Front for the Protection of the Syrian People).
Like other al-Qaeda affiliated groups, al-Nusra's statements and videos are usually issued by its own media group, al-Manara al-Baida (the White Minaret) in Syria.
Al-Nusra has claimed responsibility for several attacks against the Syrian army, security and shabiha (state-sponsored thugs) since it announced its formation early this year.
This particular group's attacks increased from seven in March to 66 in June, according to its own statements.
In order to assess al-Nusra's abilities and its geographical reach, I analysed 128 attacks between March and June for which it claimed responsibility in formal statements, and which have been recognised by jihadist forums as genuine.
Findings show that jihadists are operating actively in urban areas; 54% of attacks took place in the capital, Damascus, and 20% in the second city of Syria, Aleppo.
Other areas in which jihadists have operated include Deraa (17% of attacks) and Deir al-Zour (about 6%). Other areas account for 3% of attacks.
"The jihadists' ideology contradicts with what the FSA is fighting for," Col Nimah told the BBC. The latter are fighting under the banner of democracy and a civil state rather than sharia.
However, the difference between the two parties in their modus operandi is reminiscent of the difference between Iraqi resistance groups and jihadists during the American invasion in 2003.
Are they [jihadists] good fighters? Yes, they are, but they have a problem with executions”(Saleem Abu Yassir FSA commander)
The jihadists in Syria are also using tactics that are closer to so-called "peace-time terrorism" tactics, unlike the tactics the FSA is using, which are mainly open raids and clashes.
Jihadists, in the last four months, used ambushing tactics 30% of the time, but they resorted to assassination in 23% of their attacks. Some 16% of jihadists' attacks consisted of IEDs (improvised explosive devices) and car bombs. Kidnapping and suicide bombs represented 8% and 7% respectively of these attacks.
IEDs and kidnapping were very common in Iraq. It is notable that all kidnaps committed by the groups end with the killing of the hostage, without seeking any ransom for instance.
The Guardian's Ghaith Abdul Ahad interviewed a village elder of Shahail (50 miles, or 80km, west of Mohassen in Deir al-Zour province), Saleem Abu Yassir, who is also a commander of the local FSA brigade.
He told Mr Abdul Ahad about jihadists: "Are they good fighters? Yes, they are, but they have a problem with executions. They capture a soldier and they put a pistol to his head and shoot him. We have religious courts and we have to try people before executing them."
The situation in Syria is also attracting jihadists from neighbouring countries as seen in Iraq a few years ago.
According to the New York Times, the intelligence community in the United States assesses that jihadists from the Iraqi branch of al-Qaeda are expanding to Syria.
In a video message last February, al-Qaeda's leader Ayman al-Zawahiri called on militants in Iraq, Jordan, Lebanon and Turkey to rise up and support what he called "their brothers in Syria".
Jihadist forums announce the death of foreign fighters in Syria on a frequent basis - from Saudi Arabia, Lebanon, Egypt and so on. The authorities in Jordan have arrested a couple of jihadists trying to sneak into Syria.
Other jihadist factions are operating on the ground.
Beside the local small groups such as Ahrar al-Sham, other jihadist groups such as Lebanon-based Fatah al-Islam which clashed with Lebanese authorities in 2007, and the Abdullah Azzam Brigades, which claimed responsibility for several attacks against Israel from south Lebanon since 2007, have shown a presence in Syria.
Al-Qaeda-affiliated jihadists, however, agree with the FSA in the short term; it is unlikely this agreement will last in the long run if the influence of jihadists increases.
23 March 2012 Last updated at 18:15 GMT
Q&A: Syria sanctions
The international community has imposed wide-ranging sanctions on President Bashar al-Assad's regime, in an attempt to put pressure on the Syrian government to stop using violence against demonstrators.
The Arab League, European Union, United States and Turkey have all imposed economic sanctions on Syrian individuals and companies. In March, First Lady Asma al-Assad became the latest person connected to the regime to be targeted for sanctions when EU foreign ministers imposed a travel ban and asset freeze on her.