File Photo: Members of the Islamic State militant group. (Associated Press)

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Islamic State militants have killed three Assyrian Christian captives who were among nearly 200 Christians abducted earlier this year in northeastern Syria, two human rights monitoring groups said today.The three men were killed late last month but the news emerged this week when a video showing their deaths was released, the Britain-based Syrian Observatory for Human Rights reported.The Assyrian Human Rights Network said the three men were among 187 Assyrians being held by Islamic State. Both organisations said they were killed two weeks ago on Eid al-Adha, an Islamic holiday.Islamic State abducted the Assyrians in February during battles with the Syrian Kurdish YPG militia in northeastern Syria.