Defence Secretary Des Browne has said Afghanistan should not be allowed to return to a "haven for terrorism".
The UK took over peacekeeping operations in May
Mr Browne, who is in the country, made the call following the death of a British soldier during clashes with suspected Taleban forces in Helmand.
The soldier, the first killed in action since UK troops were sent to the province in May, was from 7 Parachute Regiment Royal Horse Artillery.
Mr Browne sent his sympathies to the family calling it "great sorrow".
The Ministry of Defence had contacted the soldier's next of kin but released no other details, saying the family had wanted 24 hours to inform other relatives.
Some 3,300 British troops are acting as part of a Nato-led peacekeeping force.
Two other British soldiers were also badly wounded in the incident.
Mr Browne said: "I wish to express my sincere condolences to the families and friends of those killed and injured in this attack.
"My thoughts are with them and those troops continuing their difficult task of helping to ensure Afghanistan remains secure.
"Along with about 40 other countries, we're here in Afghanistan determined to make this a safer place for the people of Afghanistan to live in."
'Haven for terrorism'
Mr Browne also said the country should not be allowed to return to being a place of refuge for terrorists.
"We must achieve our objective of making this a better country not only for the Afghan people, but also we mustn't allow it to become a haven for terrorism again," he said.
"There are people out there after three decades of conflict who are determined to stop us doing that; they'll deploy any violence that they can to stop us doing that but they can't be allowed to succeed."
The Ministry of Defence said a mobile patrol was engaged in a fire fight in Sangeen, a small town taken from Taleban control earlier this year by Afghan security forces backed by US air power.
British Apache helicopter gunships were called in to support the troops and Afghan sources said several Taleban soldiers were killed in the fighting.
BBC defence correspondent Paul Wood, who is in Afghanistan, said Taleban fighters have been taking refuge in the surrounding countryside following the town's capture in February.
"The Taleban have since retreated to the hills but pose a constant threat to coalition forces," he said.
"What British commanders are trying to prepare people to accept is that not only is it going to be difficult over the next few weeks and months, but it may take quite a long period of time to make a difference here."
Meanwhile, a coalition spokesman said a bomb hit a US armoured vehicle in a village in Ghazni province in the east of the country on Sunday, after a shoot-out with suspected Taleban fighters.
Elsewhere in Ghazni, gunmen shot dead three people on Saturday night, officials said. In Kandahar province four road workers were also killed.