|The UK has about 9,500 troops deployed in Afghanistan, the bulk of which is in Helmand [EPA]
The UK prime minister, visiting Afghanistan on an unannounced trip, has said British troops could start withdrawing from the country as early as next year.
David Cameron said improving conditions made him optimistic about the withdrawal.
"In terms of next year I think that it is possible. We have to deliver on the ground what's necessary. What I have seen today gives me cause of cautious optimism," Cameron said on Tuesday.
Cameron has earlier made clear he hopes all British troops will be out of Afghanistan by 2015.
Talking at Camp Bastion in Helmand province on Tuesday, the prime minister also shrugged off US and Afghan criticism of the troops' performance, saying it no longer held true.
In a US diplomatic cables released by WikiLeaks, American diplomats in 2008 said diplomatic troops deployed in the Taliban stronghold of Helmand were "not up" to the task of securing the province.
Another cable said Gulab Mangal, the Helmand governor, had told US officials in January 2009 that American forces were urgently needed.
"When you look at what was said, it was relating to a previous period, when we all know now there weren't enough troops in Helmand," Cameron told reporters.
The UK has about 9,500 troops in Afghanistan, the bulk of which are in Helmand, where they were spread thinly until the US deployed an extra 30,000 troops to the country. Officials have said British troops have been able to concentrate on smaller, strategic areas of Helmand since the extra US troops
"The force density issue ... you can absolutely feel it on the ground, it makes a difference," Cameron said.
He said the US criticism of British efforts in Afghanistan had not damaged ties between the two countries.
"I think the British-American relationship is incredibly strong ... of course WikiLeaks has led to lots of embarrassing questions but I think in the end it just doesn't change any of the fundamentals between Britain and America," he said.
At a conference in Portugal last month, Nato leaders agreed to meet the timetable set by Hamid Karzai, the Afghan president, for foreign troops to end combat operations in Afghanistan by the end of 2014.
Despite the presence of about 150,000 foreign troops in the country, civilian and military casualties are currently at their highest level since the Taliban were ousted in 2001.
At least 346 British troops have died in Afghanistan since 2001, almost a third of them this year.
Casualty rates among foreign troops have risen dramatically, particularly in the south and east, since July 2009 as Nato-led forces mounted more operations against the Taliban and other anti-government fighters.