BAGHDAD, Iraq (AP) U.S. troops sweeping through Fallujah on Thursday said they believe they have found the main headquarters of the insurgent group headed by Jordanian terrorist Abu Musab al-Zarqawi.

In video shot by an embedded CNN cameraman, soldiers walked through an imposing building with concrete columns and with a large sign in Arabic on the wall reading ''Al Qaida Organization'' and ''There is no God but Allah and Muhammad is his messenger.''

Inside the building, U.S. soldiers found documents, old computers, notebooks, photographs and copies of the Quran...

... The senior U.S. Marine commander in Iraq cautioned that the discovery by soldiers in Fallujah was still being investigated.

''I cannot stand here and tell you that we found the command and control house or building where Zarqawi went ahead and orchestrated and dealt his (car bombs) ... and the other death and destruction that he has spread throughout the country of Iraq,'' Lt. Gen. John Sattler told reporters at the Pentagon in a video teleconference from Fallujah. ''We will continue to look for that.''

Also, Sattler said the U.S.-led offensive launched last week in Fallujah has ''broken the back of the insurgency'' by seizing their main base of operations.

''We feel right now that we have, as I mentioned, broken the back of the insurgency. We've taken away this safe haven,'' he said.