James Foley's captors sent his family a rambling email threatening to kill him just a week before making public a video of his execution, the American reporter's employer says.
GlobalPost on Thursday released the full text of the email from Islamic State of Iraq and Levant(ISIL) militants "in the interest of transparency and to fully tell Jim's story".
"We believe the text offers insight into the motivations and tactics of the Islamic State," it added.
The release followed the media outlet's revelation that Foley's captors had demanded a ransom of 100 million euros ($A142.82 million) for his release.
The email claims "other governments" had accepted "cash transactions" for the release of hostages and says the militants offered prisoner exchanges for Foley's freedom, naming Aafia Siddiqui, the scientist jailed for 86 years for attempting to murder US military officers.
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ISIL, which has marauded across large areas of Iraq in recent months, published a video showing one of its members beheading Foley on Tuesday.
Foley, a photojournalist, was reporting from Syria for GlobalPost and other outlets including AFP when abducted in November 2012.
Prior to disclosing the email, CEO Philip Balboni said the captors made contact with GlobalPost and the Foley family fewer than half a dozen times, and "the kidnappers never really negotiated" over their huge sum, but simply made their demand.
"We never took the 100 million (euro) figure seriously," he told CNN.
The US government opposes paying such ransoms, arguing that it only encourages more hostage-taking.
"We do not make concessions to terrorists. That includes: We do not pay ransoms," State Department deputy spokeswoman Marie Harf told reporters on Thursday.
Balboni referred to the release of several European hostages by the extremist group earlier this year, likely upon payment of ransoms that were "dramatically less" than what the group sought for Foley.
The family and GlobalPost were seeking to raise money "in the range" of the amount paid for the other hostages, Balboni added, without mentioning a dollar amount.
Harf referenced the other countries' ransom payments to the group, saying that in 2014 alone, they amounted to millions of dollars, although she too did not provide a figure.
And she stressed that the US government "does not have contact with ISIL".
Balboni said he and the family provided all information about their search for Foley and their contact with his captors to authorities at the FBI and State Department.
