"It's a tough nut, whether or not bringing in more troops, more US troops will have a signifcant long term impact on the violence," Casey said at a news conference here with US Defense Secretary Donald Rumsfeld.

He spoke after meeting at the White House with President George W. Bush, who expressed confidence in Casey's advice despite the worsening violence.

Describing the situation in Iraq as "difficult and complex," Casey acknowledge that sectarian violence in recent weeks is as high as it has been since the US invasion in 2003.

"If you add the intensities of Ramadan and the fact that the new government is just standing up, this makes for a difficult situation that's likely to remain that way for sometime," he said.

He said bringing it under control "is going to be a long-term process. It's not going to be something that we're going to get done quickly."

And he said ultimately it would require an Iraqi solution.

Casey described the Shiite extremists, death squads and militant militia groups as "the greatest current threats in Iraq."

However, he said progress was being made and the broad strategy of standing up Iraqi security forces to eventually take over from US troops was still "a valid framework."

Casey added that the situation was under constant review and he was making changes as necessary, citing his decision in July to forego planned troop cuts and to keep a beefed-up force in Iraq instead.

"And so we constantly look at what we need, and I ask for what I need," he said.

Asked whether he needed more troops, Casey said, "Right now my answer is no. But we're continuing to work things back there. If I think I need more, I'll ask for more and bring more in."

He said there was no question that more troops has some effect in bringing down levels of violence in local situations.

"But whether more US troops for a sustained period will get us where we're going faster is an open question, and that's part of the calculations that I make as I go through this," he said.

Earlier, the chief of staff of the army said his service has enough troops in its planned force rotations to maintain current troops levels in Iraq through 2010.

But General Peter Schoomaker questioned how long the army can sustain its current deployment of 23 brigades worldwide, including 15 in Iraq.

"For any foreseeable contingency right now we have enough brigades. But what would the cost of that be?" he told reporters.

"The cost would be to freeze people in place and to surge. That's not desireable to me. I don't think that's desireable to any of us, over having the ability to sustain a rotation base," he said.

US commanders already have had to extend the year-long rotations of some units in Iraq to quell the onslaught of sectarian violence.

Schoomaker said the army needs continued access to the national guard and reserve to sustain the force.

Asked whether the current pace of deployments to Iraq can be maintained without loosening limits on the use of the guard and reserve, Rumsfeld would not say.

But he said the military "is looking at these various sensitivities. And we're looking around corners up ahead and asking ourselves how we would do things."

Schoomaker noted that the Pentagon strategy calls for having 18 or 19 army brigades available for deployment at all times.

"So how many do we have right now? Twenty-three," he said. "So where are they going to come from? Well, they come from turning them faster. So you get less dwell time than we want under the strategy."

"Dwell time" refers to the length of time a unit has at its home base resting, reequipping and training, versus the length of time it is deployed.

"The strategy says we should have two years dwell time for the active force (for every year deployed). We don't have two years dwell time. We've got a little over one year dwell time right now," Schoomaker said.

"That's part of the shock absorber you have there. Now the question is can you do that for a long time?"

Related Links
Iraq: The first techonology war of the 21st century