Syria has become an intractable, violent mess in the last three years. And understanding the conflict there is particularly tough since reporters have only limited, and dangerous, access to the country.

Syrian journalist Muhammad Ali slipped into his war-torn country from Turkey for our partner PBS Frontline despite the obvious risks. He traveled with fighters of the Free Syrian Army (FSA), who originally were fighting against the regime of Syrian President Bashar al-Assad. Now, the rebels are fighting Islamic jihadists, many from outside the country, who are taking control of areas in Syria and imposing their own rule.

The FSA fighters told Ali to hide his identity by wearing scarves and staying out of view, for his own protection. Because Ali is Syrian himself, he would be treated just like other rebel fighters, the FSA told him. “We cannot guarantee your life.”

And some American and European journalists reporting in Syria have been kidnapped by the Islamic State of Iraq and Syria (ISIS) jihadists.

Ali traveled with the FSA fighters as they tried to take back a small town called Al Atareb from the ISIS fighters. He says, “it’s the first time in Syria or even the Middle East that moderate fighters are fighting back the jihadists.”

“The ISIS fighters control a lot of territory north of Aleppo and Al Atareb is strategically very important for the FSA,” he explains. If ISIS controls the town, they will be able to keep the rebels under seige and will control the north of Syria. Then, he says, the FSA will be "stuck between the jihadists in the north and the regime forces in the south."

So this battelfront is key for FSA rebels and stakes are high. The Frontline documentary includes a video shot on someone's cell phone showing ISIS executing seven FSA rebels.

Ali says the rebels were captured in Aleppo and taken to Al Atareb where they were executed. “It was a show of strength, the jihadists executed them in viewing distance of other FSA fighters.”

He was present when the FSA fighters launched a raid on an ISIS position, killing some of the ISIS fighters and chasing away others. Ali says the ISIS fighters can be defeated, but "it’s going to be long battle. The FSA fighters just don’t have enough weapons to defeat the jihadists and fight the regime [government] troops at the same time."

His new report, Syria's Second Front, airs on PBS Frontline starting on February 11, 2014.