Isis supporters say the group has publicly beheaded three men on charges of homosexuality and blasphemy.
Pictures circulated by accounts affiliated with the group show a man kneeling on the floor behind a fighter brandishing a knife. In a third image, a man can be seen reading from what is understood to be a charge sheet.
Other punishments advocated by Isis include amputation, crucifixion and stoning.
The images are believed to have been taken in Nineveh province, in Iraq, although the specific location and date remains unknown. Isis overran parts of Nineveh, including the capital Mosul, in June last year and continues to target religious minorities living or trapped there.
Images depicting similar atrocities are regularly published by the extremist group in its defacto stronghold of Raqqa. There, militants have thrown men accused of homosexuality from buildings and stoned any to death who survive the fall. The most recent killing was committed on Tuesday in front of a huge crowd.
Disturbing images released this week saw the group hanging bodies at a checkpoint in the Iraqi district of Hawija. Some analysts said the brutal display was likely an attempt to distract from losses suffered in nearby Tikrit.
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