You scan the alleys and the three-storey buildings directly across the rooftop, you search for a gunman, a sniper crouched by a wall or window, in the shadows. If you see a gun muzzle flash, you shoot.

These are some of the thoughts flashing through the minds of US marine infantry crouched on the frontline of the grinding day-to-day battle for Ramadi, the capital of the turbulent western province of Al-Anbar.

"You get kind of numb to it after a while," says Lance Corporal Kris Mazel,

"War does some scary stuff," he says, commenting on the deadening of troops' emotions as they fight an urban war in this city of 400,000 people.

Almost every day, about 30 marines are stationed in the al-Anbar government headquarters, home to US-backed local officials tasked with skippering the region through the chaos and tumult of the post-Saddam Hussein era.

The L-shaped two-storey structure is heavily scarred by mortars. Its date palm trees have shrivelled and trash litters the shrubs and brown dirt.

The surrounding buildings are pockmarked by shells, with gaping holes flanking signs advertising a young businessmen's club and grocery stores.

Shrouded in brown web-like camouflage netting, marines sit in their five sentry posts constructed from plywood and sandbags on the government building's rooftop.

The marines keep watch there for 24 hours in the fight to prop up the local government, which presides over both Fallujah and Ramadi, the two cities considered the heart and soul of the insurgency.

"For us Ramadi is the key," says Lieutenant Nathan Braden, a marine spokesman.

Ramadi and Fallujah appear to be on the brink of possible US-led offensives to wipe out the Sunni Muslim insurgency ahead of scheduled January national elections.

US army and marines have roped off Fallujah since mid-October and escalated air strikes there.

Officials in Ramadi told AFP the marines expected to increase the number of troops in the provincal capital in the coming days.

"We are putting more forces inside the city proper," says Major Mike Targos, the executive officer for Second Battalion-Fifth Marines.

"There is a repositioning of forces."

Until now, the 2-5 marines, numbering close to 1,000 men, have cruised the streets and maintained eight combat outposts across the city. The US army has patrolled the edge of eastern Ramadi and its northern suburbs.

At least 20 US troops have been killed and more than 130 others wounded in the area since September when the 2-5 battalion returned to the country for the first time since the 2003 American-led invasion of Iraq.

"Since we've been here there's been a rise" in the violence, Targos says.

Every day, at the government centre, the marines brace for the worst. On Friday, at least two mortars struck the compound, wounding two marines and an Iraqi security officer.

Lance Corporal Matthew Soto, 23, stares out from his sandbag post, 400 to 500 metres away from an alley where minutes earlier, a fat woman shrouded in a black veil apparently lugged guns into an apartment.

"At night time that's when things go down," he says, sitting behind his 5.56 calibre steel black machinegun.

The marines keep a vigilant eye on the local Iraqi national guard and police assigned to the perimeter of the facility, especially after dark.

Some Iraqi special forces, tasked to the government centre, warn the marines that the national guard will flee their posts minutes before an attack as if they had already been given a heads up by the rebels. They caution the national guard may be in cahoots with the insurgents.

The spectre of death has drilled fatalism into the young marines.

"Whatever happens, happens. It's fate. If God wants to see me, if it's my time, I can't fight it," says 20-year-old Lance Corporal Joe Sutton.

Drawing home the point, Sutton talks about an incident six week ago when the marine who had taken over his shift on the government centre roof was shot dead by a sniper.

"Someone was screaming we need a Medevac. I was shaking," he says.

The normally swaggering and tough-talking Sutton swears he did not tremble from fear.

"The way it goes one night is totally calm, the next night it's hell," he adds as he watches the hours slowly tick by in the building, considered a flashpoint in the war for al-Anbar's future.