The presence of British troops in Afghanistan has "energised" the Taleban, the defence secretary says.
Six Britons have died in the Helmand province in the last month
Des Browne said the "scale and nature" of the opposition became clear when UK troops were first deployed to Helmand.
He told the Guardian the overall aim of the mission remained the creation of a "security space" for reconstruction.
He is "urgently considering" sending reinforcements to Helmand province, in the south, where six UK servicemen have died in the last month.
Private Damien Jackson, 19, became the latest soldier to lose his life in the region when he was killed in a firefight at a helicopter landing pad on Wednesday.
Mr Browne told the Guardian: "It is certainly the case that the very act of deployment into the south has energised opposition... the scale of that opposition and the nature of that opposition became apparent when we were deploying."
He said the objective of the UK deployment was clear.
"It is to let the writ of the Afghan government run in the south, against a background that these provinces have been largely lawless for three decades, leaving the Taleban, drug warlords and militia to act with impunity and brutalise local communities."
He said if the Taleban were presenting a different message to local communities, then that could put soldiers at risk.
"If the message of confusion... is played back by the Taleban into local communities, and then they think the British troops are coming to starve them or attack them, then that is putting our soldiers at a level of unnecessary risk," he said.
Former Labour defence minister Doug Henderson has called for British troops in Afghanistan to be withdrawn to barracks until a "clear political strategy" is agreed.
Conservative MP James Arbuthnot, a member of the Commons Defence select committee which has just returned from a visit to Helmand, said British troops needed more resources.
"There is a feeling of everything being run just a bit on a shoestring, but that's something that the British have always been extremely good at.
"It's just, I think, a little unfair to ask the British troops to do things on a shoestring when so much rides on us getting this right.
"We've got to succeed in Afghanistan."
His fellow committee member, Labour MP Dai Havard, said military planners had not underestimated the Taleban.
"They've gone into places that nobody's been before, and they've got into skirmishes and wars that they didn't understand were going on.
"And some of these are tribal conflicts. They're conflicts about power relationships. And they've wandered into the middle of them."