Geneva - In a blustery square across the street from the United Nations headquarters in Geneva, five Syrian women stood silent and still, each holding an elegantly framed photograph.

Just minutes earlier, a scattered group of activists and journalists had watched as the women exited the fortified UN compound and solemnly proceeded into the adjacent square. They had managed to secure a midday meeting with UN Syria envoy Staffan de Mistura, despite the chaos surrounding the first day of the latest round of Syria peace talks.

Their goal was to pressure de Mistura into bringing the issue of Syrian detainees to the forefront of his discussions with the government and opposition. Each woman held up the image of a loved one disappeared by Syrian government forces over the course of the six-year war.

Bracing herself against the strong winter wind, Amina Kholani, a former prisoner herself, eventually broke the silence.

"We are Families for Freedom," she said. "We are Syrian families demanding freedom for all the country's sons and daughters. Our position is against enforced disappearance and arbitrary detention by the Syrian regime and all parties to the conflict."

Kholani, a mother of three from the Damascus suburb of Daraya - once the heart of the uprising in the capital - has not seen or heard from her three brothers since they were arrested by government forces in July 2011. The last rumour she heard, in 2013, was that they were being held in the government's Saydnaya prison, notorious for the use of torture and systematic executions.

Her group has asked de Mistura to pressure the Syrian government and opposition to "immediately release a list of names of all detainees, along with their current location and status, and to immediately stop the practice of torture and mistreatment". They also called for the release of death certificates and reports detailing the causes of death for those who died while in detention.

There is no estimate available on the number of those killed while in government or opposition detention during Syria's six-year war, which has killed nearly half a million people overall and displaced nearly half the country.

After putting an end to the spilling of blood in Syria, [the case of detainees] should be the first issue on the table. Fadwa Mahmoud, demonstrator

But rights groups have long attempted to detail the organised and widespread nature of state-sponsored abductions. As of 2015, more than 65,000 people had been forcibly disappeared by members of the state security apparatus in an "organised" and "systematic" campaign to silence dissent, according to a report by Amnesty International

Enforced disappearance refers to the abduction of a person by state agents, who then conceal the person's whereabouts and deny them legal protection. Both Amnesty and the UN have said the scope and scale of the practice in Syria amounts to a crime against humanity.

"This is a group of mothers, of sisters, of wives … We all have someone in detention," said Fadwa Mahmoud, a life-long political dissident and former detainee who has not heard from her husband or her eldest son in four years.

Her husband, political activist Abdel Aziz al-Khayer, was held more than four years ago along with her son, Maher, on their way home from the airport. At about three in the afternoon on September 20, 2012, Maher called his mother to let her know that they were en route home.

"After five minutes - I'll never forget that day - but I felt I needed to call him again, just to make sure he was okay," Mahmoud told reporters in Geneva. "When I tried again, the phone was off … and from that day, I've heard nothing about where they were taken or what happened to them."

She believes that members of the Syrian Air Force Intelligence abducted her family members, noting that she has spoken with officials from the UN, the Red Cross and the European Union in an effort to find out more information, but to no avail.

"I've met de Mistura several times, and I met Brahimi before him. Neither of them could tell me anything," Mahmoud said, referring to Lakhdar Brahimi, the UN's previous Syria envoy.

Even after years of fruitless searching, the 63-year-old refuses to quit: "We're only a group of five women here, but we have thousands supporting us in Syria. It's different when politicians claim to speak on our behalf. We are the ones that represent the real people, not the politicians."

Mahmoud, who also serves as an adviser to the opposition's High Negotiations Committee, is hopeful that collective pressure could bring matters to a head.

"We want an accumulated effort that includes the largest possible number of families, irrespective of their loyalties. If they have someone detained, we want them to stand with us and to be part of our group," she said, noting that the families can support each other, as they have experienced the same trauma.

De Mistura, who participated in a brief moment of silence with the women on Thursday inside the UN compound, later told reporters that "you can be sure that we will be constantly raising detainees, abducted and missing people" during the talks.

"There are thousands and thousands of mothers, wives, daughters … who are hoping that at least this aspect will be one of the benefits of any negotiations," de Mistura said.

At the same time, Mahmoud acknowledged the slipping ceasefire in Syria and the low expectations of forging any substantive agreement in Geneva.

"[The politicians] speak about the case of detainees as if it's a side issue … but after putting an end to the spilling of blood in Syria, it should be the first issue on the table," she said. "There's no question about it."