The Britain-based Syrian Observatory for Human Rights reported Wednesday that the women were freed from a Damascus government building. It said they were released Tuesday, and hadn't been able to contact them.
The women may have been released as part of a three-way exchange reached earlier this week. It saw Syrian rebels release nine Lebanese men held for a year and a half. Lebanese gunmen simultaneously released two Turkish pilots held since August. Lebanese officials said some imprisoned Syrian women were to be released to meet rebel demands.
It's unclear how many women are held by Syria's government, nor how usual it is for 13 to be released simultaneously.
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