BEIRUT -- The past week of clashes between a segment of Syria's rebellion and a gang of jihadist militants has benefited the only rebel faction there to be formally designated by the United States as a terrorist organization, experts say.
The faction, Jabhat al-Nusra, or the Nusra Front, is chiefly known for its links to al Qaeda and was deemed a terrorist group by the State Department in December 2012. Nusra officially pledged loyalty to al Qaeda's leader, Ayman al-Zawahiri, in April.
But the group's role in the recent conflict has complicated that picture, particularly from the perspective of frustrated Syrian activists, who increasingly have watched Nusra emerge as a less-hostile, more indigenous alternative to the Islamic State in Iraq and al-Sham (ISIS).
Westerners and many Syrian activists hope the current round of battles, which pits much of the former Free Syrian Army against several ISIS battalions, will put an end to ISIS' behavior. In recent months, ISIS has infuriated the opposition by imposing harsh Islamic law across already liberated parts of the north, leading to the kidnapping and detention of many Western journalists, Syrian activists and doctors.
Officially, Nusra has portrayed itself in the current struggle as an above-the-fray mediator. On Tuesday, its leader, Abu Mohamed al-Jolani, called for an immediate ceasefire.
But the statement also condemned ISIS for what it called "incorrect policies," and urged the group to release prisoners it has been holding -- a major grievance for the FSA battalions. It called for all factions to refocus on "the fight against the regime."
And on the ground, Nusra's actions have been even harder to divine.
"Jabhat al-Nusra's role is a complex one," said Aymenn Jawad al-Tamimi, a researcher at Oxford who has closely followed the back and forth inside Syria.
In some cases over the past week, such as in Deir Ez-Zor, Nusra elements have been "protecting ISIS" from the rebel assault, al-Tamimi notes. In Raqqa, a brigade affiliated with Nusra appeared to join in the fight against ISIS.
Because it has not wholeheartedly joined the fight alongside its ideological counterpart, Nusra has won the tentative praise of Syrian activists. "They've earned new respect among the local population for their participation in the campaign against [ISIS], and this can be seen clearly among activists who have taken to praising Al-Nusra," said Shakeeb al-Jabri, a Beirut-based Syrian activist and analyst.
Like many activists HuffPost has spoken to in Lebanon and Turkey over the past couple of months, al-Jabri emphasized that while he does not support Nusra's religious or political platforms, he would not be surprised to see many secular Syrians back Nusra because its main objective is defeating the forces of the regime of Syrian President Bashar Assad.
"The U.S. should note that in the future, should they want to take any action against Al-Nusra, even the most liberal of Syrians are likely to side with the group, despite differences of ideology," al-Jabri said.
The transformation is vexing for Western policymakers, who still seek reliable allies in the ever-shifting landscape of Syria's uprising.
U.S. officials have in recent months expressed openness to meeting with all rebel groups, including members of the recently formed Islamist Front, whose ideas closely mirror the principles of Nusra or ISIS, but who have sided with the Free Syrian Army in the latest fighting.
In conversations with HuffPost, however, those officials also drew an inflexible demarcation against dealing with any groups formally designated as terrorists, like Nusra. (Several officials hinted that a designation of ISIS was likely soon.)
"The line is clear," one State Department official said. "If we've designated them, we're not meeting them."
Meanwhile, Nusra units have emerged as some of the best-equipped and most effective units in the fight against the forces of Assad.
In a recent article in the National, an activist in the south claimed that in some cases, major battlefield victories claimed publicly by the FSA are really made by Nusra. He said this is frequently obscured in order to keep from frightening away Western backers of the rebellion.
"The FSA and Al Nusra join together for operations but they have an agreement to let the FSA lead for public reasons, because they don't want to frighten Jordan or the West," the activist told the paper.
And as ISIS has risen to prominence, so has Nusra's reputation as a potential counterbalance -- one that, crucially, was seen as largely domestic in origin, unlike ISIS, which consists of a large number of foreign fighters.
"After its founding, ISIS seemed to pull away most of Jabhat al-Nusra's foreign fighters, which solidified the idea of ISIS as a predominantly foreign group and Nusra as a predominantly Syrian one," said James Le Mesurier, a director at the Turkey-based group Analysis, Research and Knowledge.
As the current round of fighting dies down, Le Mesurier added, many of those fighters will realign themselves, and it remains to be seen how that will shape Nusra's future ambitions.
"Both [Nusra and ISIS] have recruited among Syrians and foreign fighters," he said, "and as a result of this fighting we're seeing defections of both Syrians and foreign fighters from ISIS to other brigades."
"Nusra stands to gain from ISIS' undoing," said Joshua Landis, a professor at the University of Oklahoma who focuses on Syria. "Many of the ISIS fighters will either have to leave the country or go over to Nusra."
Whether that means a stronger, if tamer, version of Nusra emerges or one that simply seeks to replace ISIS as the predominant rebel faction, is anyone's guess, the experts say.
Concern about the latter possibility -- that Nusra might attempt to impose Islamic law across the north, rather than focus on the anti-Assad fight -- has kept many Syrian activists from fully embracing the group.
"What ISIS did, may just be repeated by Nusra after they get more and more fighters from around Syria," one Turkey based Syrian activist told HuffPost. "And then it will be difficult or impossible to stop them."