Her family has asked that she not be identified.
Details of the abduction and ransom demand were shared Monday with ABC News by Mauri Saalakhan of the Peace and Justice Foundation and a family friend of the unidentified American hostage.
According to the information provided, the American woman was kidnapped sometime in 2013 while in Syria as a humanitarian relief worker.
The terrorists are reportedly seeking in addition to the $6.6 million ransom the release of Siddiqui,a female neuroscientist trained at MIT, who was convicted in 2010 for attempting to kill U.S. officials. She was arrested in 2008 in Afghanistan in possession of notes referring to dirty bombs, sodium cyanide and a list of land marks in New York City. During her interrogation, the BBC reported she allegedly got hold of a rifle and opened fire, shouting "death to Americans."
Supporters of Siddiqui's family said they were "very distraught" to hear that IS was involving her in their ransom demand. A statement from the Siddiqui family read: "If the issue is true, we would like to state that our family does not have any connections to such groups or actions... We believe in a struggle that is peaceful and dignified. Associating Aafia's name with acts of violence is against everything we are struggling for."
The Siddiqui family has written to the IS militants to underline that "these are not the conditions under which we want our loved ones released," Saalakhan said Monday, adding that IS should release the young aid worker "without any strings attached... And the right thing would be to let this young woman go back to her family, go back to her life. And the right thing for America to do, for our government... would be do the same with Dr. Aafia Siddiqui."
The female aid worker is one of at least four American hostages reportedly held captive by IS. Journalist Steven Joel Sotloff appeared briefly in an IS video released last week that showed the beheading of photojournalist James "Jim" Foley.