Thousands of troops currently earmarked to cover for a firefighters' strike are being withdrawn from that role to be ready for military operations.

In announcing the move, the Ministry of Defence (MoD) insisted that no decision had yet been taken on a possible strike against Saddam Hussein.

At least 10,000 soldiers plus people from the RAF and Navy have been allocated to man Green Goddess fire engines in the event of a national firefighters' strike.

The MoD has announced that almost 3,000 of those troops will be taken off fire duty to be ready for what it calls "potential military operations".

We must ensure we are able to respond to any requirement that may be placed on us

MoD

The units involved in the shift include the 1st Battalion of the Black Watch, the Royal Scots Dragoon Guards, the 1st Battalion of the Royal Regiment of Fusiliers and the 1st Battalion of the Irish Guards, as well as artillery, engineers and logisticians.

They are largely front-line troops from the joint rapid reaction force on red alert for action.

They will be replaced on fire strike duty by other units held at lower readiness.

The MoD said it was "prudent contingency planning to allow these higher readiness units to continue with military training and give us the flexibility to undertake operations if required".

"We must ensure we are able to respond to any requirement that may be placed on us," a spokesman added.

Army 'Green Goddess' fire engines may soon be in the streets

It is also the first move by the British military that can be clearly linked to potential action against Iraq.

And shadow defence secretary Bernard Jenkin told the BBC's Today programme it would send an important signal to Baghdad.

The move comes a day after Foreign Secretary Jack Straw told MPs they would get a proper vote on possible military action.

However, he said it would not be possible to put down a motion immediately or shortly before military action commenced if the effect of that were to give the enemy advance notice of any attack.

The British Army is not big enough to have 10,000 soldiers out of action and not feel the effects

Liberal Democrat defence spokesman Paul Keetch

He added that Tony Blair and his ministers shared the anxieties of the Labour rebels who voiced their opposition to war with Iraq.

However, he said the government believed the threat of force was the best chance of getting a peaceful resolution to the Iraqi crisis.

The military currently has commitments ranging from Sierra Leone to Afghanistan alongside a staffing shortfall of more than 7,400.

Last month, in talking about sickness levels among soldiers, Paul Keetch, the Liberal Democrat defence spokesman said: "The British Army is not big enough to have 10,000 soldiers out of action and not feel the effects."

And in April Defence Secretary Geoff Hoon admitted that "We (the Army) are at the limits of our commitments".

Strike ballot

Over the next few weeks up to 55,000 firefighters will be voting on strike action after the Fire Brigades Union rejected a 4% pay offer.

The union is calling for a 40% pay rise, to give fully-qualified firefighters a �30,000 annual wage.

The employers have made an interim offer of 4%, tied to changes in working conditions, which has been rejected by the FBU.

The union has called for a ballot of its members for strike action.

The results of the strike ballot will be announced on 18 October.