US officials say they could not confirm that an American woman hostage had already been killed.

National Security Advisor Susan Rice made the statement after Islamic State militants claimed that the woman, identified as 26-year-old aid worker Kayla Mueller, had been killed by Jordanian fighter bombs.

She said the US government remains committed to the policy of not negotiating with terrorists over hostage issues.

"We don't make concessions to terrorists and to hostage takers. We don't pay ransom. We adhere to that policy rigorously because it is our strong view, and our experience that when you make concessions and you pay ransom, you are only generating greater incentive for additional acts of hostage taking and you are providing resources to fuel those continued operations and horrific attacks."

Mueller was the last-known American hostage held by Islamic State, which has executed five British and American aid workers and journalists in recent months.

The IS claimed that Muller died when the building in which she was being held collapsed in a Jordanian air strike early on Friday.

Jordan intensified its bombing of IS strongholds following the release of a video showing one of the country's pilots was burnt alive in a cage, a practice that insulted Islamic sensibility or Hadith.

Meanwhile, Rice also reaffirmed that America would not have major shifts in the military campaign against Islamic State militants in President Barack Obama's new national security strategy.

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