The group calling itself the Brigades for Defending the Holy Sites named the intelligence officer as Usama Abd Al-Jabbar.
The video tape showed the officer revealing his personal information to his captors.
The armed group was also heard saying in the tape the capture was in response to the current fighting in Najaf city.
Iraqi troops killed
Earlier, an Iraqi national guard commander in Samarra was shot and killed along with a senior aide.
Lieutenant-Colonel Ihsan al-Saji and Captain Saddam Husayn were killed on the main highway north of Baghdad as they travelled to the capital, an interior ministry official said.
Al-Saji had "made a lot of enemies" following repeated US-led anti-resistance operations in Samarra, most recently on Saturday.
In a flier distributed in Samarra, the Ahwaz branch of the Islamic Secret Army said it carried out the killings and threatened similar attacks against other Iraqi security forces personnel.
"We cut him to pieces and scattered the remains on the road ... those who continue to work for the occupation forces will experience the same fate"
Ahwaz branch of
the Islamic Secret Army
"We cut him to pieces and scattered the remains on the road," the group said. "Those who continue to work for the occupation forces will experience the same fate."
The attack came hours after a senior US commander warned his troops would not hesitate to launch further operations against resistance members, like Saturday's joint air and ground assault in which the US military said 50 were killed.
"If we find enemies in Samarra, we will strike, because it's good for people of Samarra and it's good for people of Iraq," said Major-General John Batiste, commander of the 1st Infantry Division.
In a meeting with Batiste, provincial governor Hamid Humud Shakti asked US troops to reopen a bridge in the city, but the general refused until "terrorists and foreign fighters" leave Samarra.
We have "tens of millions dollars in projects in Samarra, but you won't get a dime as long as the city is not working hands to hands with the coalition", he said.
Earlier on Monday, a US tank was destroyed by an explosion in al-Sadr city in Baghdad.
A US military spokesman said an explosive charge detonated on the tank, but the Shia al-Mahdi Army said it had hit the tank with a rocket-propelled grenade.