A Syrian rebel group said Monday that Damascus had failed to free dozens of female detainees who were supposed to have been released from regime jails as part of a weekend hostage exchange.
The Northern Storm brigade, based in the north of Syria, had expected the prisoners' release after they freed nine Lebanese Shiite pilgrims kidnapped 17 months ago.
Two Turkish pilots taken hostage in Lebanon in August were also freed as part of the deal.
"We sent a delegation representing both us and the women (detainees), as well as Syrian Muslim scholars, to welcome the women at the agreed time in Adana airport (in Turkey)," but no one arrived, said the Northern Storm brigade.
Northern Storm agreed to release the nine Lebanese men under a deal brokered with Turkish, Qatari and Lebanese mediation.
On Saturday, Lebanese authorities repeatedly thanked Damascus for accepting the rebels' demand to free 100 to 200 women detainees held in regime jails.
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A day earlier, Lebanese Interior Minister Marwan Charbel had said a senior security official who secured the deal would hand over a list of some 200 women detainees to Damascus, and that the Syrian authorities were "cooperating very well" on the issue.
But since then Syrian authorities have made no official statements on the matter.
Northern Storm also stressed "the need for efforts by all sides to ensure the women prisoners are freed immediately, and to relieve the Syrian people's pain with their return to their families and children".
The group's statement said a deal had been in the offing for some time, but that an Al-Qaeda front group's advance in its area of operations in Aazaz, northern Syria, forced it to act more quickly.
"Because of an Islamic State of Iraq and the Levant occupation of our bases, we were forced to hasten the exchange," said Northern Storm, which battled for weeks to halt ISIL's advance.
Northern Storm also denied receiving any payment in exchange for the hostages, "as some provocative Lebanese media had claimed".
Tens of thousands of people are being detained by the Syrian regime, many of them without trial, activists say.