The captors pledged not to kill the men but threatened to kill any national guard it might capture in future.
The videotape shows armed men with their faces concealed, pointing guns at a group of men wearing Iraqi national guards uniforms with their backs to the camera.
Aljazeera is unable to confirm if the captured men on the tape are indeed members of the Iraqi national guard.
In other developments, 10 Iraqis, four of them policemen, were killed and 20 others wounded, including the correspondent of Kuwait News Agency, in a car blast that targeted an Iraqi police checkpoint in Zyona district in central Baghdad on Wednesday.
Meanwhile, a previously unknown group, Ansar al-Jihad, has threatened to execute three captured relatives of interim Iraqi Prime Minister Iyad Allawi after 48 hours if the government fails to halt the assault on Falluja.
The Iraqi troops are said to have
In a statement published on a website, whose authenticity Aljazeera cannot vouch for, the group claimed responsibility for seizing the three relatives of Allawi on Wednesday.
The official spokesman of the Iraqi interim government, Thayr Al-Naqib, named the three as Ghazi Allawi, a cousin of the prime minister, his wife and son. They were snatched outside their home in Yarmuk district in Baghdad earlier in the day.
Also on Wednesday, the Association of Muslims Scholars, an influential Muslim body, reported that one of its members, Shaikh Abd al-Wahab al-Janabi, has been killed in the ongoing US-led assault on Falluja.