By Middle East analyst Nick Pelham

As Washington unveils plans to deploy hundreds of US troops in Yemen, American officials are already surveying the Arabian peninsula terrain ear-marked for the next war on terror.

We're not Red Indians and this isn't the Wild West

Yemeni tribal Sheikh

On a hushed visit late in February, US ambassador to Yemen, Edmund Hull, ventured 160km east from the fortress of the US embassy in the capital Sanaa into the mountainous hinterland.

Western diplomats believe the region is fast becoming the Arab world' s prime hideout for al-Qaeda fighters.

In the shadow of the Queen of Sheba's Bilquis temple, tribesmen tightened the grip on their Kalashnikovs as Mr Hull's motorcade sped past in a dust-ball towards a military hospital.

Wild West

"We're not Red Indians and this isn't the Wild West," spat a turbaned sheikh, as he jabbed his AK-47 into two blinded camels dragging millstones which grind sesame seeds into oil.

Backed by leading Islamic radicals, Yemen's tribesmen are vowing to defend their domains against an American incursion.

President Saleh has swapped attacks on the tribes for negotiations

The people are proud that their rose-red mountains - and a stretch of Saudi Arabia to the north - is the only territory in the Arab world to escape Western colonisation.

They accuse the US of plotting a covert war to wrest control of the country's mineral wealth.

An American company found an oil basin near Maarib in 1984. Today Maarib ranks as one of Yemen's richest oil-fields, but receives crumbs from the cake.

Al-Qaeda refuge

"There's a risk for the US if it starts disturbing the tribes," warns Yemeni academic, Faris al Saqqaf.

In October 2000, Yemenis who the US says are linked to al-Qaeda blew up the American naval ship, USS Cole, docked in Aden to the South.

The USS Cole was attacked in Sanaa harbour in October 2000

At least two of the wanted - Mohammed Hamdi al-Ahdal and Ali Qaed Senyan al-Harthi who Washington claims are linked to al-Qaeda - have found refuge with Maarib's sheikhs.

Western diplomats believe quelling Yemen's tribes is a key stage on the road to US victory against al-Qaeda, many of whose fighters - like the Osama Bin Laden family - originate from Yemen.

The World Bank is funding a large road-building programme to extend central government's authority into landscape as rugged as Afghanistan's.

And the US embassy's mission to Maarib was intended to earmark aid projects for the development and pacification of Yemen's most troublesome - or independent - province.

Guns and aid

Guns accompany the promise of aid.

On visits to Sanaa last month, General Tommy Franks, the US commander-in-chief co-ordinating the war on terror, CIA Director George Tenet and FBI Director Robert S Mueller all squeezed President Ali Abdullah Saleh to reverse his earlier opposition to the deployment to Yemen of scores of US military advisors and FBI agents.

Ambassador Hull visited Aden amid preparations for the reopening of refuelling facilities for the US Navy in Aden.

Yemeni tribesmen in Maarib are expected to resist Yemeni and American operations against al-Qaeda

Yemen - once the only Arabian Peninsula state without an American base - has now taken centre-stage in America's al-Qaeda hunt.

Fearing the war on terror is turning into an attack on their autonomy, the sheikhs, too, appear to be readying for a showdown.

Observers say the 1994 civil war, when the northern sheikhs vanquished the south, has left Soviet tanks and hardware in the hands of the tribes.

Sheikhs against terror

In December, tribesmen repelled a Yemeni Special Forces raid to capture al-Qaeda suspects. Eighteen government troops were killed.

Since then, the president has traded combat for negotiation - tribal-style.

When Yemeni security forces detained me for a few hours in Maarib (reporting is not welcomed there), I was locked in a high-walled courtyard adjoining a cell holding the four young sons of tribal chieftains.

The boys claimed to have been kidnapped.

They said they would remain jailed until their fathers sign the UN-sponsored pledge titled "Sheikhs against Terror" and handed over al-Qaeda suspects named on an American list.

"The sheikhs simply don't take us seriously unless we take them or their relatives hostage," explained a senior official.

Yemenis have a name for President Ali Abdullah Saleh's governance - tribalocracy.

For more than two decades, the tribes shared his power, and in return guaranteed his survival.

Even in the presidential palace, tribal law is as likely to hold sway as parliament. It's a unique way of life.

But to Washington, it is the mark of a failed or failing state - and a magnet for Bin Laden's fugitives.

If the US has its way, Yemen will now be saying goodbye to all that.