Militants staging attacks in Iraq are as strong now as they were a year ago, America's top soldier has said.
Myers insisted the number of attacks did not reveal the full picture
Between 50 and 60 attacks are carried out each day, the same number as in 2004, according to Gen Richard Myers, chairman of the joint chiefs of staff.
But he added it was too early to say if a recent surge in violence amounted to a concerted campaign, and insisted that US-backed forces were "winning".
A BBC correspondent says US optimism after the Iraqi elections has now gone.
The US Secretary of Defence, Donald Rumsfeld, said the key to winning the insurgency was ensuring that the political process in Iraq took hold.
Speaking of the insurgents who have waged a campaign of violence since the invasion by coalition forces in 2003, Gen Myers said:
"I think their capacity stays about the same. And where they are right now is where they were almost a year ago."
The past week in Iraq has seen a welter of attacks, with dozens dead in suicide bombs and a civilian helicopter brought down outside Baghdad.
Gen Myers said that just counting the number of attacks was in any case a poor method of measuring the insurgency and pointed out that half of attacks were thwarted.
Reports of car bombs come in nearly every day from across Iraq
"I think we're definitely winning - I think we've been winning for some time," he said.
Nonetheless, the BBC's Adam Brookes at the Pentagon says, it is clear that the optimism or even euphoria that gripped America's military leadership after the success of the Iraqi elections in January has now dissipated.
The view from Washington is that success in Iraq now depends on the new government in Baghdad and whether or not it can entrench itself and become a cause that Iraqis will deem worth fighting for, our correspondent said.
Mr Rumsfeld said he did not believe it would be the efforts of US and coalition forces that proved decisive in the battle against the insurgents.
"The people that are going to defeat that insurgency are going to be the Iraqis," he said.
"And the Iraqis will do it not through military means solely but by progress on the political side and giving the Iraqi people a sense that they have a stake in that country."