DAMASCUS, Syria -- Um Hassan earns a little over $10 for a day's work as a freelance housekeeper. She travels by bus from her home on the outskirts of the Syrian capital Damascus to her clients' homes, usually near the city center.

She says the money, equivalent to the average salary of a government worker in Syria, often goes toward food and school supplies for some of her grandchildren. She has nine. On occasion, she says she indulges her own youngest child, a not-yet- married teenage daughter, with a new dress.

But last month, the life Um Hassan has always known was disrupted as the Syrian civil war intensified, and she was unable to go to work.

"We were warned that the Shia were coming to kill us," she said in an interview in Damascus. "We locked our doors and stayed inside for three days. I didn't let any of the children out. We really believed they were coming to massacre us!"

Um Hassan, which means "mother of Hassan," a common way of calling a parent by the eldest son's name, is a Sunni Muslim. She lives in a mixed but mainly Sunni neighborhood located near Sit Zeinab, a major Shia Muslim shrine on the outskirts of Damascus.

When she and her neighbors finally ventured out of their homes, they were relieved to learn that there had been, after all, no massacre of Sunnis.

"Thank God, nothing happened," said Um Hassan. "But when we started talking to our Shia neighbors, we discovered that they, too, had heard the same warning about us! They thought we were planning to go massacre them. They locked themselves at home just like we did."

It was not clear to Um Hassan who had initiated the rumors, or why. But she was clear on what had happened.

"It was fitna," she said.

Fitna is an Arabic term that is difficult to translate into English. Dictionaries define it in many ways, from infatuation to sedition, but in the Islamic tradition it refers to igniting suspicion, usually of a sectarian nature.

Spreading fitna seems to be the latest threat undermining Syria's rebellion from within.

This is what Ayman, a 40-year-old theater critic and longtime dissident, believes. He said he did not want to use his real name because he has already "lost too many friends" who condemn his criticism of what they call The Revolution, and accuse him of sympathizing with the Bashar al-Assad regime.

He explains that he always challenged the regime, and certainly does not condone its behavior in the conflict, now in its 17th month. He just feels put off by Syria's rebellion because of the fitna he says it is introducing.

"Never in my life here in Syria have I heard people ask are you Sunni or Shia. But now, just the other day my friend of 20 years asked me that for the first time," he said.

"Imagine, all this time we've been friends, he didn't even know that I was neither Sunni nor Shia. He didn't know that I was Christian! It never came up and it never mattered.

"But now he tells me 'Oh, it's because you're Christian, you're a regime supporter.'"

Ayman added that long ago he used to organize student protests when people were "too scared to even breathe." He was referring to the reign of Hafez al-Assad, the current president's father and a close Soviet ally who ruled Syria with an iron fist.

"So of course I'm not a regime sympathizer. But I do blame the opposition for introducing a sectarian and revenge-based narrative."

The conflict in Syria has been growing more violent and revenge-driven. Last week, members of the Free Syrian Army in the embattled city of Aleppo posted footage of more than a dozen men they had captured. The men were all from the same clan, the Al Berri, known for their loyalty to the Assad regime and accused of acting as Shabiha, or pro-government thugs. Their captors accused them of breaking a ceasefire and killing 15 members of the FSA.

In the video, the FSA fighters line up their prisoners against a wall and summarily execute them in a barrage of bullets. The execution sparked controversy within the ranks of the opposition.

The head of the Syrian Human Rights Observatory called it "criminal," and social media swelled with criticism of the field execution.

"You say you killed men who themselves raped and pillaged and killed innocents," said one activist. "But all I saw was you killing half-naked and defenseless prisoners, one of them elderly."

"Two wrongs don't make a right," raged another.

These complaints, along with Ayman's and Um Hassan's, may not have fallen on deaf ears. Some activists and fighters are now pushing for a higher standard of behavior.

The Local Coordination Committee, a loose group of Syrian opposition activists, issued a protocol and published it on its Facebook page, inviting the numerous and independent battalions that make up the FSA to sign it.

The protocol calls for fair treatment of prisoners. It pledges, among other things, not to cause bodily or psychological harm -- in other words, torture -- in order to extract information, something the regime has long been accused of doing.

Within hours, about half a dozen battalions signed it.

One battalion took the further step and posted a video on YouTube (in Arabic, with English subtitles) of its commander pledging to adhere to the Geneva Convention.

But the FSA has no central command, and there are still dozens of independent battalions that have probably not heard of this protocol. They receive funding from various sources, many based abroad. They make their own decisions on the battlefield, where they fight against the regime's tanks and aerial bombardment with little more than light weapons.

Without central coordination, it might be difficult to expect the rebels to take the high road in the face of a brutal regime that is itself accused by the international community of war crimes, including torture and field executions.

"That's the problem," said a Damascus-based activist who goes by the nom de guerre Mohammad Raslan. He condemned the field execution of the Berri clan.

He said the ideal solution is to coordinate among the many FSA brigades, but that would require a network of secure communication.

"And that's something we don't have," he said.

Indeed, what they have instead, is a growing sense of suspicion towards their neighbors and the very real possibility that religious bias and violence may yet end up influencing the outcome of Syria's tortured revolution.