Kayla Mueller may have been given to an Islamic State fighter as a bride during her captivity, sources within the US intelligence community say.

CNN reported on Wednesday that US intelligence officials spoke to them in condition on anonymity that there are intelligence reports that Mueller may have been an ISIS bride when she was being held by the extremist group.

However, the intelligence official said that information is unclear on whether she was "coerced, sold or forced" into being an ISIS bride.

The National Security Council moved to debunk that statement through a press release of its own. The NSC said that investigation is ongoing, but such reports are mere speculation.

"Reports that have been published by certain news outlets regarding Kayla's time in (ISIS) captivity are speculative and unproven at this time," spokeswoman Bernadette Meehan told the media through the statement. 

"The US government continues to analyse any information regarding Kayla's captivity but has not corroborated any of the multiple theories regarding the conditions throughout the duration of her captivity," she added.

Islamic State published a statement on Friday declaring that Mueller was killed during a Jordanian airstrike in Raqqa. The ISIS also published a photo of the rubble of one of the buildings that were destroyed in the airstrike.

The Mueller family subsequently issued a statement directly to the Islamic State requesting it to provide them with evidence of Mueller's death.

According to the New York Times, Islamic State responded and sent a private message to Mueller's family over the weekend with enough pictures to enable them and forensic examiners to identify the hostage, which had been in captivity since 2013. 

The New York Times also revealed that one of Mueller's post-mortem images showed her with a bruise, and that the people who viewed the photos doubted that her injuries "were consistent with being killed in the rubble of a flattened building."