Syria's brutal conflict may not see a lasting solution until the fate of tens of thousands of detained civilians is disclosed, rights groups and activists said on Wednesday.

Since the Syrian war erupted in 2011, more than 330,000 people have died, millions have been displaced, and tens of thousands arrested or forcibly disappeared across the country.

"Lasting peace in Syria will be impossible without resolving the issue of detainees," Syrian activist and former detainee Fadwa Mahmoud told AFP on Wednesday.

Her husband Abdulaziz al-Kheir and son Maher Tahan disappeared in Syria nearly five years ago, and Mahmoud has not heard from them since.

"If there's 'peace' and my son and husband are still arrested -- you think I'm going to behave?" said the short woman with a curly, silver pixie haircut.

Mahmoud spoke on the sidelines of an art exhibit in Beirut organised by Amnesty International to mark the International Day of the Victims of Enforced Disappearances.

The belongings of detained Syrians -- glasses, wallets and keychains -- were on display along with testimonies of the people they belonged to.

Mahmoud said she felt politicians and negotiators working on peace in Syria had not prioritised the fate of detainees.

"This issue needs to be of the first degree. We must not forget it -- those detained cannot do anything, so we must act."

- 'This should not be ignored' -

Thousands of peace activists were arrested after Syria's conflict first broke out in 2011, and many are still languishing in prisons, according to non-governmental organisations.

Amnesty researcher Diana Semaan said that uncovering details on their fate was becoming increasingly difficult with each passing day.

"It's becoming more and more challenging," she told AFP.

"If now these families don't know where their loved ones are, there's always a risk they might never know where they are."

Human Rights Watch also warned that failing to resolve the detainee issue could prevent a real solution to Syria's six-year war.

"Syria will not be able to move forward if negotiations fail to adequately address the horrors of detention and disappearance," said Sarah Leah Whitson, Middle East director at HRW.

Last year, a team of UN experts raised the alarm over enforced disappearances and called for the situation to be referred to the International Criminal Court.

"This should not be ignored. Without progress, each day that passes will likely see more of the disappeared tortured or executed," Whitson said.

HRW called on Wednesday for an independent enquiry to probe the fate of thousands of people who have disappeared in Syria's war and to identify mass graves.

"An independent institution in charge of investigating the fate and whereabouts of the disappeared, as well as unidentified human remains and mass graves in Syria, should be created immediately," it said.

The New York-based rights watchdog said the enquiry "should have a broad mandate to investigate, including by reviewing all official records and interviewing any official".

Earlier this month, the death of prominent computer scientist Bassel Khartabil Safadi was confirmed two years after his execution by the regime.

Safadi had been arrested in March 2012 in the wake of the crackdown

Source: AFP