Aljazeera aired a brief video on Tuesday showing Carroll speaking to the camera, without broadcasting her voice.
The Qatar-based station said the kidnappers identified themselves as members of a previously unknown armed group the Brigades of Vengeance.
Aljazeera reaffirmed its rejection of all forms of violence against journalists and demanded Caroll's immediate release.
Carroll, 28, was working for The Christian Science Monitor and was abducted earlier this month. Her Iraqi interpreter was killed.
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.
Carroll's former employers The Jordan Times published a Sunday editorial, stating: "The kidnappers who abducted her could not have chosen a more wrong target. True, Jill is a US citizen. But she is also more critical of US policies towards the Middle East than many Arabs… Jill has been from day one opposed to the war, to the invasion and occupation of Iraq. "
There has been a spate of kidnappings of Westerners in Iraq over the past few months after a lull during most of 2005.
"Jill has been from day one opposed to the war, to the invasion and occupation of Iraq"
The Jordan Times
Four Christian peace activists - a Briton, an American and two Canadians - are still being held captive. A French engineer is also being held.
Carroll is the 31st journalist to be kidnapped in Iraq since the start of the war in March 2003, according to Paris-based Reporters Sans Frontieres, a media advocacy group.