"It's really impossible to speculate on how large the number is," says Lama Fakih, Human Rights Watch's Lebanon and Syria researcher, who has been talking to alleged victims throughout the camps.
"There's an issue of underreporting from victims of sexual abuse – there's fear of retaliation."
Rights workers tracking the issue have started to hear a flood of second and third-hand reports of rape flooding from the thousands of refugees who have fled besieged Idlib and Aleppo for border camps.
The stories paint a horrifying picture.
"The army will come in, bomb a town and then [they'll] come through, loot houses and rape women," says Lauren Wolfe, the director of Women Under Siege, a Women's Media Center initiative on sexualized violence in conflict.
Wolfe tells of a number of video reports featuring women who say they've been raped and men who have confessed to raping women. She adds that those confessions, usually from Syrian army defectors now detested by forces loyal to Assad, "are possibly under duress."
Sexual violence after military operations
"The pattern we've seen," Fakih says, "is that it's happening in areas after large scale military operations. Most reports now are coming out of Homs."
One medical worker told Human Rights Watch that there had been several victims in each hospital she had been in.
"There'd be heavy shelling in an area, and then the army would come in, and into women's homes," Fakih said.
Elsewhere during the Arab Spring, rape was used widely by soldiers loyal to Moammar Gadhafi in the later stages of Libya's civil war. It has traditionally been one of the crueler tactics of war used by dictators intent on terrorizing, demoralizing and subduing a rebellious population.
Soldiers carrying out the act typically go untried.
"What characterizes sex abuse in Syria is that there's a total impunity," Fakih says.
"Everyone indicated that perpetrators had not investigated, had not been penalized in any way. We also interviewed defectors who indicated that people in their units had participated in sexual abuse and nothing had happened to them."
Workers suspect the problem has been occurring since the early stages of the country's civil war.
Wolfe and her team have heard stories of Syrian women in Turkish camps who talked about being sexually abused while in Syrian detention.
As early as last November, a man coming from Aleppo said that while detained, he had heard women in the facilities being sexually abused.
Both Fakih and Wolfe say it is impossible to speculate on the number of victims inside Syria. The country has made it impossible for journalists or rights workers to secure visas, with most restricted to border camps or forced to sneak into the country illegally, on foot, mainly from points near the southern Turkish city of Antakya.
Rights workers have been left to rely on second and third-hand reports.
Wolfe's team has seen more than 80 reports of sexual assault. These include rape at checkpoints manned by Assad soldiers, and in detention.
In the latter cases, she has heard of men being raped, or wives are brought in and raped in front of them.
Some reports contained more than one incident. One particular case featured the rape of three sisters. Thirty six women were raped in another.
No exact figures
"I've heard that the numbers could be in the thousands, but I can't [properly] estimate," she says. "In my work reporting rape in conflict, I've found that for every one woman who comes forward [with her story], there are 10 women behind her [who will not.] And in this case there's no motive for women to speak out. They're not getting more medical or psychological care out of it."
"We've had a real rush for a while, of information coming in," Wolfe adds. Workers are now focusing on the intense fighting between Assad's forces and rebel fighters in Aleppo, one of the country's larger cities and an Assad stronghold that could soon be controlled by rebels.
Stories of rape, she says, "trickle out when the fighting dies down, and I'm concerned that could be the case in Aleppo – that we start hearing a tremendous number of reports."
Human Rights Watch is "absolutely concerned it will continue," Fakih adds, "because of the total impunity. Nothing we've seen indicates that these soldiers have anything restraining them, and unless that happens I expect this will continue."