The posting, on a Web site that frequently carries militants' statements, included a photo of what that statement said was an American soldier, wearing desert fatigues and seated on a concrete floor with his hands tied behind his back.
But the authenticity of the statement and photo could not be verified, and Liam Cusack, of the toy manufacturer Dragon Models USA, Inc., said the image of the soldier portrayed in the photo bore a striking resemblance to the African-American version of its "Cody" military action figure.
"It is our doll ... to me it definitely looks like it is," Cusack said. "Everything the guy is wearing is exactly what comes with our figure."
He said the figures were ordered by the U.S. military in Kuwait for sale in their bases, "so they would have been in region."
In Baghdad, Staff Sgt. Nick Minecci of the U.S. military's press office in Baghdad said "no units have reported anyone missing."
The figure in the photo appeared stiff and expressionless.
In the photo, a gun barrel was pointed at the head of the man's figure, and behind him on the wall was a black banner emblazoned with the Islamic profession of faith, "There is no god but God and Muhammad is His prophet."
A statement posted with the picture suggested the group was holding other soldiers.
"Our mujahedeen heroes of Iraq's Jihadi Battalion were able to capture American military man John Adam after killing a number of his comrades and capturing the rest," said the statement, signed by the "Mujahedeen Brigades."
The posting did not show any ID card for the alleged captive and no organization's name was written on the black banner, as have appeared in some past claims of kidnappings. The man's uniform had no U.S. insignia or names visible.
The Mujahedeen Brigades have claimed responsibility for two kidnappings in the past — the abduction in April of three Japanese who were released and that of a Brazilian engineer who went missing after an ambush that the Brigades claimed to have carried out along with the Ansar al-Sunnah Army.
More than 180 foreigners have been kidnapped in the past year. At least 10 of them, including three American civilians, remain in the hands of their kidnappers.
The only American soldier known to have been taken hostage is Pfc. Keith M. Maupin, 20, of Batavia, Ohio, who was shown in a video in April being held by militants. Another video aired in June showed what purported to be Maupin's slaying, but the picture was too unclear to confirm it was him and the military still lists him as missing.
Marine Cpl. Wassef Ali Hassoun went missing in Iraq in June and later photos surfaced on Arab television showing him blindfolded with a sword to his head. In July he made his way to the U.S. Embassy in Beirut. Back in the United States, he said he had been captured, but in December he was charged with desertion for the incident.