A secret incident report about the abductions, written by Najwa Fatih-Allah, the director general of the data processing center where the five Britons were seized, quotes Gen. David Petraeus, the U.S. commander in Iraq, as saying the Mahdi Army "will be profoundly sorry" if it carried out the assault.
The militia is the armed wing of radical Shiite cleric Muqtada al-Sadr's political movement. The firebrand al-Sadr only recently returned to Iraq after about four months hiding in Iran, apparently to avoid trouble during the U.S.-Iraqi security crackdown in Baghdad.
Meanwhile, as CBS New chief foreign correspondent Lara Logan reports, a big part of the U.S.-Iraq security crackdown involves handing over more power to the Iraqi Army. But with so many officers who served under Saddam Hussein now filling the top army ranks, Iraq's prime pinister admits there is a real threat of a coup.
"There are some of them who are still loyal to the previous regime and they are making problems," Prime Minister Nouri Al-Maliki told Logan in an exclusive interview. "Sometimes they even violate the security of military operations."
"I am not afraid but I have to watch the army because those still loyal to the previous regime may start planning coups," added al-Maliki. "Those people don't believe in democracy and for that reason we are monitoring the status of the army very carefully."
Portions of the incident report about the abductions were read to The Associated Press on the telephone by a government official who did so only on condition of anonymity because the document was not for public distribution.
A top Interior Ministry official, who refused to be named because he was not authorized to speak to the media, said suspicion immediately fell on the Mahdi Army because it was in control of the area and would have blocked such a massive operation by any other group.
Fatih-Allah's report to Finance Minister Bayan Jabr said four men in civilian clothing appeared at the center about 10:45 a.m. Tuesday, 15 minutes before the kidnapping.
The account said the four men claimed they were from the government anti-fraud commission and looked through each room in the center, then quickly left the building.
At about 11 a.m. dozens of men in army and police uniforms, the report said, burst into the building, disarmed guards and went directly into the room where the five Britons were working. The five were seized, rushed out of the building to 19 waiting four-wheel-drive vehicles and the convoy drove away to the east.
The building sits on a side street off Palestine Street, a major thoroughfare in eastern Baghdad and not far from Sadr City, a stronghold of radical Shiite cleric Muqtada al-Sadr's Mahdi Army.
In other developments: