New York-based rights organization also on Wednesday called on the militants to release the civilians.

It said that the group was captured in the coastal province of Latakia during a militant offensive a year ago.

Another group of 40 hostages was released in May as part of a deal that allowed Syrian opposition forces safe passage out of the besieged Old City of Homs.

But the group of 54, which includes 34 children, was still being held, apparently "with the intention of compelling government actions, including exchanging the hostages for detainees in government custody," HRW said.

"For a year families have been waiting to be reunited while rebel groups and the government negotiate over their fate," said HRW's Middle East and North Africa director Sarah Leah Whitson.

"Civilian lives are not pawns for fighters to trade. The hostages should be let go immediately."

It is unclear which groups are holding the 54 captives, with HRW saying at least 20 separate terrorist forces took part in the Latakia offensive last August.

HRW said it had identified several individuals, mostly from Persian Gulf countries, who had fundraised for the Latakia operation and warned that citizens or countries that backed groups involved in hostage-taking could be complicit in war crimes.

The group also repeated its call for the situation in Syria to be referred to the International Criminal Court.

“Referring Syria to the ICC would send a clear message to all combatants that they must abide by the laws of war," Whitson said.

Syria has been gripped by deadly unrest that killed more than 170,000 people since 2011. According to reports, the Western powers and their regional allies - especially Qatar, Saudi Arabia, and Turkey - are supporting the militants operating inside the country.

NGD/BA