"Iraqi militants holding a man they say has a German passport have called on Germany to release Muslims imprisoned in its jails," Aljazeera said on Thursday.
"The group calling itself Protectors of Islam Brigades is holding Abd al-Hussain al-Zaidi, who in the video called on the German government, Chancellor Gerhard Schroeder and German media to quickly intervene for his release," Aljazeera said, showing a video of al-Zaidi and two masked fighters behind him.
Aljazeera said it obtained the videotape from the Associated Press news agency.
Most Germans and Chancellor Gerhard Schroeder were staunchly opposed to the 2003 US-led war on Iraq.
More than 130 foreigners have been seized in Iraq over the past 18 months. Most have been freed after negotiations or the payment of a ransom, but about a third of them have been killed.
Many more Iraqis have been abducted, often for ransom.