A woman kidnapped a year ago has been identified as one of the American hostages being held by the Islamic State (IS), formerly known as the Islamic State of Iraq and al-Sham.

IS demanded $6.6 million and the release of a Pakistani prisoner being held in the United States in exchange for the release of the woman, whose identity is being withheld.

The 26-year-old American was on a humanitarian mission in Syria in 2013 when she was kidnapped. Also being held by the terrorist group is Steven Sotloff, a journalist who appeared in a video released by IS last week. The video also showed the execution of photojournalist James Foley, who had been missing for nearly two years.

In addition to the ransom, the extremist Muslims demanded that Aafia Siddiqui be released. Siddiqui was convicted of attempted murder and assault of U.S. officers in September 2010, and sentenced to 86 years in prison. She was also accused of possessing bomb-making instructions, sodium cyanide, a list of U.S. targets for a "mass casualty attack," and other incriminating items when she was arrested in Afghanistan in 2008. The neuroscientist has also been accused of having ties to al-Qaeda.

Siddiqui and her supporters deny the charges against her, and her family said they were "very distraught" that her cause is being sullied by IS.

"If the issue is true, we would like to state that our family does not have any connections to such groups or actions," a letter from Siddiqui's family read. "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.

"While we deeply appreciate the sincere feelings of those who, like us, wish to see the freedom of our beloved Aafia, we cannot agree with a 'by any means necessary' approach to Aafia's freedom. Nor can we accept that someone else's daughter or sister suffer like Aafia is suffering."

ABC News reported that in addition to the unidentified woman and Sotloff, there is at least one other American being held hostage by IS.