US troops have discovered a huge insurgent bunker complex dug into a quarry in western Iraq, with air conditioning, showers and a large stockpile of weapons, the American military said.

The Marines said the complex was 170 meters (yards) wide and 275 meters long, making it one of the biggest insurgent hideouts discovered in Iraq. They said nobody was in the bunker when it was found.

"Within the various rooms making up the facility, Iraqi security and coalition forces discovered four fully furnished living spaces, a kitchen with fresh food, two shower facilities and a working air conditioner," said Captain Jeffrey Pool of the 2nd Marine Division.

"In one portion of this insurgent lair, coalition forces and Iraqi security forces found numerous types of machine guns, ordnance including mortars, rockets and artillery rounds, black uniforms, ski masks, compasses, log books, night vision goggles, and fully charged cell phones."

The bunker system was close to the town of Karma near Falluja, around 50km west of Baghdad.

Iraq's western Anbar province is the area of Iraq where the insurgency is strongest -- more US troops have been killed there than in any other province. Most of the

province is desert, and the overwhelmingly Sunni Muslim population is concentrated mainly in towns along the Euphrates River.

The US military says al-Qaeda's network in Iraq brings weapons, cash and foreign Arab fighters into the country through the western border with Syria.

Foreign suicide bombers stay in a succession of safe houses in Anbar on their way to launch attacks, officers say.

Falluja was controlled by insurgents for several months last year after the US military pulled its troops out of the city. Following an offensive to drive out guerrillas in November, Marines said they found several bomb-making factories, guerrilla training centres and buildings where hostages were kept.

AP adds: Arguably Iraq's most popular Shia group, followers of radical cleric Muqtada al-Sadr have packed away their guns and now speak of "political resistance" rather than martyrdom in battle.

Once dismissed as an upstart, the portly al-Sadr has been transformed into a respectable political figure, commanding the loyalty of key lawmakers and several Cabinet ministers.

"We are growing stronger and our appeal is becoming wider," Ibrahim al-Jaberi, a senior official at al-Sadr's office in Sadr City, said Saturday.