Britain's most senior general in Afghanistan has cautioned against any significant troop withdrawal until late next year, it was reported today.
General James Bucknall said the coalition had to hold on to recent gains, and should not send "conflicting signals" about its commitment.
The intervention comes amid debate over when the military surge implemented by US President Barack Obama should be wound down.
David Cameron announced earlier this month that around 450 UK personnel are to be pulled out by the end of the year, and there have been hints that further cuts could follow.
The elimination of Osama bin Laden has added impetus to calls for operations to be scaled back.
In an interview with the Daily Telegraph, Gen Bucknall - deputy to US General David Petraeus in Afghanistan - said the 140,000 Nato troops now deployed could be cut this year by trimming roles such as cooks and engineers.
But "in broadest terms", the reinforcements which arrived last year had to stay, he said.
"The coalition has had a good winter. We have got to hold on to what we have gained and hold that over this fighting season," he said.
"What we are doing is reaping the benefits of having the resources in place to match the strategy we have always had. Many of those resources only hit the ground in autumn 2010.
"We need, in broadest terms, that set of resources in place for two winters and two fighting seasons, which would mean we are talking about autumn 2012.
"This is not the time to send conflicting signals on commitment to the campaign."
There has been a spike in violence over the past fortnight as the Taliban has begun its usual spring offensive following the end of the opium poppy harvest.
Gen Bucknall said months of nightly special forces raids had weakened the insurgency by capturing or killing leaders and seizing caches of arms and explosives.
"It would be fair to say the insurgency is under greater pressure than it has ever been before but ... we expect (the insurgencies) to come back hard and their main focus of effort will likely be Kandahar and Helmand," he added.
A Ministry of Defence spokeswoman said: "Afghanistan remains our top priority. UK forces will no longer be in a combat role or in the present numbers by 2015 but may remain to train and mentor the Afghan forces after that.
"UK forces are continuing to make progress against the insurgency and also in training the Afghan National Security Forces.
"However, UK forces are in the most difficult part of Afghanistan and what we cannot do is to see a reduction in our combat troops until we are sure that we've got sufficient and lasting security."