The new head of the British Army, Sir Richard Dannatt, has warned that his soldiers can only "just" cope with the demands placed on them by ministers.
British troops are 'running at the limit of their capacity'
Speaking before 14 personnel were killed in Afghanistan, he told the Guardian troops "are fighting at the limit of their capacity".
Foreign Office Minister Kim Howells said he did not think that the British Army was overstretched.
Meanwhile, one UK soldier was killed by a suspected suicide bomber in Kabul.
Gen Dannatt, who took over from Sir Mike Jackson last week, said: "We are running hot, certainly running hot.
"Can we cope? I pause. I say 'just'."
He called for a national debate on whether enough resources are being given to the Army and said Britain was doing "more than its share of what is required in Afghanistan".
His comments were published after 14 military personnel died on Saturday when their Nimrod MR2, based at RAF Kinloss in Scotland, came down in the southern province of Kandahar.
Mr Howells, speaking from Afghanistan, said the Army had sufficient resources, but other Nato countries should be doing more.
"[Our commanders] are very confident that they have got the resources to do the job that we are here to do, and I really don't want to give the impression that there is a kind of crisis.
"It's not that, it's just that the job can be done much more quickly and I think, much more safely if it's clear that all of the Nato members in this are pulling their weight and I think that is the important thing."
He added: "There has got to be an effort right across Nato and not just concentrated on a certain number of countries like the UK and Canada."
Col Tim Collins, who commanded the First Battalion of the Royal Irish Regiment in the 2003 invasion of Iraq, said the British troops needed more resources.
"We have to ensure our troops have sufficient fire power and numbers to ensure the best chance that our servicemen will achieve their mission, and with the lowest cost in lives.
"Cutting corners and saving money, the basest of all motives, may well cost lives and could spell disaster for the UK.
"It's a very dangerous environment, nothing like what was conceived when the force package was put together."
Gen Patrick Cordingley, who was commander of the Desert Rats during the first Gulf War, said the criticism that not enough resources were being providing was justified.
"It's completely unrealistic, as some commentators are saying at the moment, that the government hasn't put enough money behind it.
"We could produce a lot more money now very quickly, but it would mortgage the future of the British Army and it probably wouldn't produce anything further for a considerable length of time."
But shadow defence minister Gerald Howarth, said the Tories had predicted that British troops would "get sucked into a very much more fierce counter insurgency operation".
However, Parliament was assured by John Reid, the then defence secretary, that this would not be the case, Mr Howarth told BBC Radio 4's World at One.