Also creating problems for the rebels as they fight against the forces of President Bashar Assad is the transition of the opposition from a force of civilians and defecting soldiers to one increasingly aligned with extremists, The New York Times reported Thursday.
Not only has the radical turn divided fighters' supporters, it has made Western nations more reluctant about arming rebels, the report said.
"They were supposed to be the people on whom we depend to build a civil society," said a civilian activist in Saraqib, a town where rebels were videotaped executing some unarmed Syrian soldiers.
The United Nations declared the act a likely war crime.
Supporters of the opposition have begun shouting slogans that not only condemn the government but criticize the rebels.
"The people want the reform of the Free Syrian Army," witnesses have reported crowds recently shouting. "We love you. Correct your path."
"We thought freedom was so near," a fighter calling himself Abu Ahmed told the Times via Skype last month from Maarat al-Noaman. "This shows it was a big lie. We cannot reach it. We can't even think of democracy -- we will be sad for years. We are losing victims from both sides."
The Syrian National Council faces a critical decision about whether it will join other groups in a more unified opposition against the Assad regime during a meeting in Doha, Qatar, the BBC said.
Western and Gulf states have been pushing for a body that would act as an agent for humanitarian and possibly military aid, the BBC said.
So far, the umbrella Syrian National Council has been the most visible opposition organization but hasn't produced a united front to oust Assad, and it has been criticized because its membership is largely based outside of Syria.
The Syrian National Initiative would replace the council and bring together Syria's external and internal opposition, the BBC said. U.S. officials have said they would like a broader opposition leadership council in which the SNC's influence is diluted.
Activists estimate more than 35,000 people have been killed since the fighting began in March 2011. The United Nations said about 1.2 million Syrians have been displaced.