Islamic State released 19 Assyrian Christian captives in Syria on Sunday after processing them through a sharia court, a monitoring group which tracks the conflict said.

More than 200 Assyrians remain in Islamic State hands, said the British-based Syrian Observatory for Human Rights, captives from an Islamic State advance last month that overran more than a dozen villages inhabited by the ancient Christian minority near Hasaka, a northeastern city mainly held by the Kurds.

Islamic State has not claimed any of the abductions. The Observatory tracks the conflict using a network of sources on all sides of the civil war which spiralled as security forces used violence to suppress protests against President Bashar al-Assad's rule in 2011.

It said 17 men and two women were released.

Islamic State has killed members of religious minorities and Sunni Muslims who do not swear allegiance to its self-declared "caliphate". The group last month released a video showing its members beheading 21 Egyptian Coptic Christians in Libya.