Here on the frontline this conflict is taking its toll on morale.

I can see the signs in the US marines I am with outside Nasiriyah.

Quite a few of the troops have said to me that this isn't what they were expecting.

They have had a tiring week of guerrilla-style fighting and it continues.

They are frustrated that their political masters gave the American public the impression that it would be easier than it's turned out to be.

But, also that they should have given them more expectation about Iraqi resistance like this.

They don't want to admit they can't deal with it, but I think there is definitely a sense that it is not the kind of fighting that they were really trained for.

One Marine told me: "I've had enough of being fired at from all directions, I just want to go home".

I thought it quite a surprising thing to say.

Appalling conditions

I think the other problem is the conditions here. There were major sandstorms earlier in the week, which created an appalling amount of dust.

I've had enough of being fired at from all directions, I just want to go home

US Marine

What has followed are Marines waking up every day in a very muddy campsite.

The dust has settled but they are surrounded by mudflats and rubbish dumps.

Some Marines are literally camped on top of garbage, and the amount of flies around at times is quite depressing.

The Marines would say that they are trained for tough conditions, so they can take this kind of thing.

All Marines eat MRE's, which are ready-to-eat meals. They come in sealed brown plastic bags, about the size of a well-padded filofax.

Three of these a day should be enough for the average Marine.

They come in all types of different varieties, beef stew, chicken with noodles, chicken with salsa, and slightly strange sounding things called formed turkey.

I've had that and I'm not totally convinced it is turkey. There are a lot of vegetarian meals, but over a long time they're boring, and they're not fresh.

Injured colleagues

On top of their poor living conditions you have to consider the effect of seeing colleagues injured, particularly after a surprise rocket attack here the other day which left 30 Marines wounded.

I was there when a lot of the injured were being brought in. Most of them had shrapnel wounds.

Some are now believed to have wounds from their own side because of friendly fire that broke out in the confusion afterwards.

But seeing their injured colleagues has undermined the mood here, and makes these soldiers feel exposed.

All around Nasiriyah is flat land, you can see Iraqi civilians walking around US positions.

Now it's come to the point that when Marines see any Iraqi civilians, they think of them as being possibly hostile. It puts them on edge.

I've been around Nasiriyah for a week, and the roads I was travelling on at the beginning of that time were thought to have little risk.

Now they're seen as very dangerous, hostile territory.

Marines travel around scanning the roadsides at all times, guns to the ready.

There are reports of renewed Iraqi resistance south of here.

Areas they've travelled through, that too is demoralising, especially to the younger soldiers.

Reinforcements

One thing that's certainly had an effect is the news that the Pentagon is deploying another 120,000 troops.

It made Marines here realise that it could be quite a long conflict.

Their style and esprit-de-corps is very strong, and they say that they can take this and fight on.

I was talking to a senior officer about the long term effect on the Marines.

He told me: "Sure they're stretched, they're tired, but they haven't been stretched to the limit yet.

"Don't think this is the end of the US Marines, just because they're receiving a slightly different type of resistance to the one they expected."