The abductors of US journalist Jill Carroll have threatened to kill her if the United States does not free Iraqi women prisoners within 72 hours, Al Jazeera television said today.
The station aired a brief video apparently showing Ms Carroll speaking to the camera, without broadcasting her voice.
The station did not say which group had claimed her kidnapping.
State Department spokesman Sean McCormack said in a brief telephone interview in Washington: "We will make every effort to work with the Iraqis to bring her back safe and sound as soon as possible."
He said he did not know if it was Ms Carroll in the video.
McCormack declined to make further comment, including about whether the United States would consider meeting the demands as aired in the broadcast.
Ms Carroll, a 28-year-old American journalist working for The Christian Science Monitor, was abducted earlier this month by unknown kidnappers who also killed her Iraqi interpreter.
Ms Carroll had been on her way to a meeting with Adnan al-Dulaimi, a Sunni Arab leader whom she had intended to interview, the newspaper had said.
There has been a spate of kidnappings of Westerners in Iraq over the past few months after a lull during most of 2005. Four Christian peace activists -- a Briton, an American and two Canadians -- are still being held captive.
Ms Carroll is the 31st journalist kidnapped in Iraq since the start of the war in March 2003, according to Paris-based Reporters Sans Frontieres, a media advocacy group.