Why Jaish Al Islam and Ahrar Al Sham are at the heart of Geneva squabbles
On Tuesday, Russian foreign minister Sergei Lavrov said his country was open to Jaish Al Islam and Ahrar Al Sham taking part in the Geneva Syria talks, but noted that Russia still considered the groups to be terrorist organisations.
Despite indications that Ahrar Al Sham would be allowed at the talks, it is unclear whether a representative of the group will be present. Jaish Al Islam, on the other hand, already has a central role in the discussions, with its leader Mohammed Alloush acting as chief negotiator for the opposition's High Negotiations Committee team in Geneva.
Russia and the Syrian government are not the only parties apprehensive about the role of Jaish Al Islam and Ahrar Al Sham in the future of Syria. While the groups both oppose ISIL, they are allies of Al Qaeda's Syrian affiliate Jabhat Al Nusra and their behaviours during the war have been seen as tinged with extremist tendencies.
Jaish Al Islam's former leader Zahran Alloush spoke of Alawites and Shiites in derogatory terms and at times advocated that they be cleansed from parts of Syria.
Last autumn, the group paraded captured Alawite civilians and soldiers through Damascus' suburbs in cages, allegedly planning to use them as human shields against government air strikes.
The group also does not shy away from gory displays of violence.
Last summer, the group released a 20-minute-long video in which its fighters - dressed in orange jumpsuits like those in which ISIL often dresses its prisoners and execution victims - executed 18 ISIL fighters by firing shotguns and assault rifles at point-blank range. By dressing its fighters in the outfits ISIL uses for its victims, Jaish Al Islam looked to present itself as turning the tables on the group. But the video closely mimicked ISIL propaganda videos, right down to its high production and portrayal of extreme violence.
Like Jaish Al Islam, Ahrar Al Sham has been accused of atrocities as well. In 2013, Human Rights Watch accused Ahrar Al Sham of taking part in executions of civilians in Latakia province alongside ISIL and Jabhat Al Nusra.
In Syria, atrocities have also been committed by the Syrian government and rebel groups typically considered far more moderate than Jaish Al Islam and Ahrar Al Sham. Observers say the Syrian government has killed far more civilians than ISIL or any other party in the war.
Alone, the groups' atrocities could likely be overlooked by those negotiating Syria's peace. But for many players - from the US, to Russia, more moderate opposition groups and others - the cooperation of Jaish Al Islam and Ahrar Al Sham with Jabhat Al Nusra makes their behaviour all the more concerning.
Both ISIL and Jabhat Al Nusra are explicitly barred from the UN-backed Syrian peace plan. But the difference is that while all of the major players of the Syrian opposition oppose ISIL, Nusra has allies who will play roles in any negotiations.
While some in the opposition may have misgivings about the influence of Jaish Al Islam and Ahrar Al Sham, the groups have carved a key role for themselves in the opposition through their military prowess.
Ahrar Al Sham fights side by side with Jabhat Al Nusra in Jaish Al Fateh, a rebel alliance created in March of last year that quickly made major gains against government forces in Syria's Idlib province.
Jaish Al Islam has earned respect by continuing to hold territory in Damascus' suburbs despite years of heavy government bombardment, representing the most powerful rebel force within striking distance of Syria's capital.
The prominence of Jaish Al Islam was also seemingly raised by the killing of its leader Zahran Alloush in an air strike on December 25. Coming in the run up to planned peace talks, Alloush's killing was viewed by the opposition as an attempt to weaken them ahead of negotiations. His brother-in-law, Mohammed, was soon given a key role by the opposition at the Geneva peace talks.
By putting its most hardline foot forward at Geneva, the opposition was perhaps matching equally stubborn moves by Damascus, which has continued sieges and bombardments even as delegates have arrived in Switzerland and given indications that it is not prepared to make concessions. For any kind of fruitful negotiations to work now, both sides will have to retreat from their more extreme positions.
This article has been updated to reflect the correct relationship between Mohammed and Zahran Alloush