Tony Blair today promised that British troops in Afghanistan would get any additional forces they needed, but said he had not yet been asked to sent more troops.

Giving evidence to the Commons Liaison Committee, the Prime Minister said that any such request would receive a positive response.

"Whenever you do a mission like this, you are constantly and so are they, the commanders on the ground, assessing what more do we need in terms of personnel, equipment, resources," Blair told the backbench MPs.

"Anything they need and ask for in order to protect our troops, I will make sure they get.

"Our obligation to them is to give them what they need to do the job, and if they come to us and say - which they haven’t so far, but which they may well do - ‘This is what we require in addition because now we’re there we can see this problem and that problem emerging’, of course we will respond to it positively."

Mr Blair denied that the British mission in the southern Helmand province had become "confused" over the various aims of combating the Taleban, supporting reconstruction and tackling the opium trade.

Five British soldiers have been killed in the past three weeks in the area.

"There is frankly a lot of nonsense talked about the mission being uncertain or people not knowing what the mission is," he said.

"The mission is to assist the Afghan government in the process of reconstruction which includes making sure that, instead of being dependent on the drug trade, their economy can grow and prosper normally.

"In order to do that, we will have to defend ourselves when attacked and take pre-emptive action if necessary. That’s precisely why we said at the time that this is a more dangerous mission."

He added: "There has never been any doubt that when you move down into the south, into the Helmand province, it was going to be a lot more dangerous. It is going to be a lot more dangerous."

Mr Blair said the work being carried out in Afghanistan by the British troops was "absolutely vital" for the future of the country and wider international security.

"If the Taleban get a foothold back in Afghanistan, then the very reasons following September 11 why we had to go into Afghanistan will all reappear with all the consequences for our own security and the security of the wider world," he said.

The commander of British forces in Afghanistan, Brigadier Ed Butler, said yesterday that he had requested some more resources, although he did not specify what.

Britain has dispatched a force of 3,300 to the lawless southern Afghan province of Helmand this year to form part of an expanding NATO peacekeeping mission, entering the most dangerous areas of the country for the first time.

Since last month, the British have been taking part in US-led Operation Mountain Thrust, billed by its American commanders as the biggest offensive against the Taleban since they drove them out of Kabul in 2001.

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