By Nick Childs
BBC Pentagon correspondent
In the wake of the recent upsurge in violence in Iraq, each day seems to have produced a new theory or report on who might be behind the attacks.
That they have become more sophisticated and co-ordinated is not in doubt, but they have left the Pentagon and US intelligence apparently uncertain as to the precise nature of the threat they are facing.
At a Pentagon news conference this week, the US Defence Secretary, Donald Rumsfeld, argued that it was too early to conclude - as United Nations Secretary General Kofi Annan had suggested - that this was a new phase in the campaign.
US forces are coming under daily attack
"It may be an isolated spike, it may have to do with Ramadan, it may have to do with an increase that will continue... none of us can predict the future," he said.
Behind the scenes, US intelligence officials can see that there is no consensus about the scope of the problem.
According to some officials, the type of attacks seen recently in Baghdad suggests an al-Qaeda connection. Others believe they are the work of Saddam Hussein loyalists, still others that a key aide of the former Iraqi leader, Izzat Ibrahim al-Douri, is orchestrating an alliance of Iraqis and foreign fighters.
The New York Times has reported that some administration officials believe the former Iraqi leader himself may be playing a significant role.
But US defence officials speaking to the BBC played down those reports.
Still, one of the key US commanders in northern Iraq, Major General Raymond Odierno, suggested in a video link-up to the Pentagon that the former Iraqi leader was still having an impact.
Many are unhappy about the US presence in their country
"What I tell everyone is, when it comes to Saddam Hussein, he was in control of this country for 25 years and there still is a bit of a fear [in] the population that he is still out there," he said.
"So I think that's the extent of his influence right now - that there's a fear that he would come back and be repressive once again."
Defence analysts in Washington suggest that the US military is paying a price now for failing to respond quickly enough, early on, to the emerging threat.
American forces are struggling to process intelligence information because they have insufficient translators, interrogators and analysts.
These problems are being addressed but that will take time.
The other main problem may be that the threat the US-led coalition is facing is not a single one but a diverse group of enemies, some of whom may be co-operating to a greater or lesser extent.