By the BBC's Frank Gardner

As US and British warships are concentrating in the region around the Gulf, local Arabs fear that a western military strike against their fellow Muslim neighbour Afghanistan is imminent.

Around 24 British Royal Navy warships as well as 23,000 British troops are gathering in Oman for long-planned exercises with the Omanis, known as Saif Sareea 2.

It's the biggest British military deployment to the Middle East since the Gulf war of ten years ago, but British officers insist that despite the rumours, it remains purely an exercise.

On the scorching deck of HMS Illustrious, Britain's most powerful aircraft carrier, Harrier jump-jets and Navy helicopters stand in neat lines, their fuselages glinting in the midday sun.

A harrier jumpjet takes off from the giant carrier

The ship slid quietly into Salalah harbour on Sunday, taking extra security precautions in view of last year's attack on the USS Cole in Aden, when suicide bombers blew a hole in its side and killed 17 US sailors.

The arrival of this aircraft carrier, Britain's primary 'on-call' warship, has added to the military options available to the planners back home.

Rear-Admiral James Burnell-Nugent, the British Task Force Commander and the most senior British naval officer in the Middle East, insists that his ships are here purely to exercise, but he admits that they offer a degree of flexibility.

Military options

That could be vital if Arab countries in the region, like Saudi Arabia, are unwilling to allow airstrikes to be launched from their soil.

"Maritime assets, ships, do have the advantage that they can operate out at sea in international waters and there isn't the same degree of dependence on the political dimension of getting approval from host countries, and that is certainly an advantage", explains Rear Admiral James Burnell-Nugent.

Operation Saif Sareea 2 will cost nearly �100m

I asked the man in charge of the carrier's warplanes, Commander Jock Alexander, if his planes could, if called upon, reach Afghanistan.

"Technically there's no reason why they couldn't go anywhere as long as we have air refuelling which we'd need to do that, " says Commander Alexander.

"Flying from the ship ourselves, the range is about 250 miles (400km) but we would expect to get air-to-air refuelling and then we could go really wherever you want. So, hypothetically, yes," he adds.

Ominous prescence

So how is all this military activity being seen by Omanis, the people hosting this exercise?

In the cafes and marketplaces of Oman, the exercises have become a common topic of discussion. Why, they wonder, are so many British troops in their country at such a sensitive time?

But most Omanis can see a distinction between British troops coming here to exercise and the idea of them going into action against a possible Muslim enemy.

People are worried, because the Americans have built up so many forces in the Gulf

Musallam, Omani student

Musallam, an Omani student says: "Omanis are used to these exercises and the presence of troops, especially here near Thumrait where there's an airbase. So we're not concerned. But when it comes to Afghanistan, definitely people are worried, because the Americans have built up so many forces in the Gulf".

Uncertain future

Arabs throughout the region are irritated that the West appears poised to strike Afghanistan without showing the world any convincing proof connecting either Osama Bin Laden or the Taleban to the attacks on America last month.

UK forces could be called upon to assist any US action

Some, like Faisal, an Omani merchant, worry that America is failing to learn the lessons from those attacks.

He says the West needs to solve Muslim grievances, such as those of the Iraqis and the Palestinians, or else the threat of terrorism will never go away.

"If it's true that Osama bin Laden did the things that happened in New York and they catch him and kill him, and they don't look for the reason why this happened, if they don't sort out the main problems in the world, then there will be many more people like bin Laden to follow", he said.

The one thing both the Gulf Arabs and the British soldiers here have in common, is uncertainty.

Nobody knows what the next step will be in America's war against terrorism, or whether the Gulf Arab states could become embroiled in a western military campaign they have no wish to join.