Progress with improving security and rebuilding in Afghanistan has been slower than hoped, Government officials have admitted.
British troops are also said to be facing increasing numbers of foreign fighters in the troubled south of the country following a series of bloody engagements.
Six UK soldiers have died in Afghanistan this month, but commanders believe hundreds of Taliban insurgents have been killed.
Officials from the Foreign Office and Ministry of Defence were speaking ahead of the publication of new United Nations figures on the Afghan poppy crop, which could be released as early as this weekend.
They confirmed the latest data was expected to show a "quite significant" rise overall. However, the picture across the country is "mixed", with production stable and even falling in some northern areas.
A senior Foreign Office official said the Taliban appeared to be increasingly turning to foreigners such as Chechens, having previously recruited among locals.
"This is beginning to change and more by way of foreign fighters - I don't mean by that Pakistanis, I mean... Jihadists - are beginning to appear," said the source.
"That, frankly, is not necessarily a totally bad sign because if the Taliban have run out of locals to to do their work for them and having to dig rather deeper to find foreigners to do it, that's not in the first instance negative."
The official admitted that progress in Afghanistan had not been as quick as people had hoped, but insisted the operation was still "on track".
"Are we on track to achieve (success)? Yes, it's probably going, as most things in Afghanistan, rather more slowly than people might have had ambition for, but it's still moving in a positive direction," he said.
