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The Islamic State militants reportedly demanded the release of a female Pakistani scientist, Aafia Siddiqui, in exchange for journalist James Foley and other western hostages.
According to The Independent, the IS militants had offered a prisoner exchange deal in a letter to the family of James Foley.
The Islamic extremists claimed that despite their offer, the US had not been interested in the deal.
Aafia Siddiqui, aged 42, is a trained neuroscientist from Massachusetts Institute of Technology (MIT) who was arrested in Afghanistan in 2008.
Siddiqui was allegedly carrying toxic substances and papers that had references to constructing a bomb and a list of cities in New York.
She was convicted of attempting to kill US military personnel and was sentenced to 86 years in prison.
