Members of the international community should provide more troops to fight the Taleban in Afghanistan, Defence Secretary Des Browne has said.
Some 86 British service personnel have died in Afghanistan since 2001
He said the demands set by commanders from Nato's International Security Assistance Force were not being met.
Mr Browne said the UK continued to ask countries for "additional support".
Meanwhile, a British soldier was killed in a battle on Saturday during efforts to recapture the southern town of Musa Qala from the Taleban.
The Ministry of Defence said Sergeant Lee Johnson from the 2nd Battalion The Yorkshire Regiment died when a blast hit his vehicle, also seriously injuring another soldier.
Mr Browne said Sgt Johnson was a "respected, dedicated professional who brought enthusiasm and humour to his work".
The death raised the toll of British dead to 86 since October 2001.
The defence secretary told the BBC Radio 4's The World This Weekend that the demands set by commanders from Nato's International Security Assistance Force were not being met.
Mr Browne said: "What is known as the requirement has not yet been met and I think that is well known.
"And we continue to discuss with our allies and our friends across the international community who can help provide the additional support that that military effort needs."
Mr Browne also acknowledged that keeping the Taleban out of parts of southern Afghanistan from which they had been driven would be an arduous task.
"This is going to be a long-term project and I do not personally feel any sense of disappointment that we have made this much progress in six years," he said.
The defence secretary said challenges remained and "the insurgency is still strong in parts".
However, wherever this had occurred, British troops had "overmatched" the Taleban.
Des Browne wants more assistance from the international community
"I believe that over this winter again, we will see another significant shift in our ability to be able to create security, which I hope the Afghans can then take advantage of," said Mr Browne.
Meanwhile, former Liberal Democrat leader Lord Ashdown has criticised the lack of international co-ordination in Afghanistan amid reports that he is just weeks away from becoming a "super envoy" to the country.
Speaking on Sky's Sunday Live with Adam Boulton, Lord Ashdown said: "I've always said that Afghanistan was more likely to succeed if the international community co-ordinated itself and spoke with a single voice.
"Its failure to do so has led us to a position I think where the relatively low level of resources we are putting into Afghanistan are seriously wasted."
The peer refused to comment on speculation that he is in pole position for a job as joint UN-Nato envoy to Afghanistan.