"A very intensive effort" is under way to find the hostages, Gen. David Petraeus was quoted as saying in the London newspaper The Times.
The captives - four security guards and a consultant - were abducted from the Iraqi Finance Ministry on May 29 by some 40 heavily armed men who took them in the direction of Baghdad's sprawling Shiite district of Sadr City. Iraqi officials have said they believe the Britons were taken hostage by the Mahdi Army militia, which is largely loyal to the radical Shiite cleric Muqtada al-Sadr.
But Petraeus was quoted as telling The Times, "It is a secret cell of Jaish al-Mahdi (the Mahdi Army). They are trained in Iraq, equipped with Iranian (weapons) and advised by Iran. The Iranian involvement here we have found to be much, much more significant than we thought before."
Speaking in Baghdad's heavily fortified Green Zone, Petraeus said of the hostages, "There have been several operations to try to rescue them, we just have not had the right intelligence," the Times reported.
Iraqi officials have said the Mahdi Army may have grabbed the men in retaliation for the killing by British forces of the militia's commander in the southern city of Basra.
The Mahdi Army has been blamed for many of the sectarian attacks in Iraq. The U.S. has long accused Iran of fueling the violence by providing weapons and training fighters.
The British ambassador to Iraq, Dominic Asquith, has appealed to the kidnappers of the five Britons to release them or open negotiations.