A UK soldier has been killed in Afghanistan's volatile Helmand province, the Ministry of Defence says.
More than 3,000 UK troops are now in Afghanistan
The soldier, from the 3 Para Battle Group, was shot while on a patrol near the town of Sangin. He died while he was being given treatment.
The incident came as Tony Blair told MPs that the UK's Afghan role was vital for world security.
A UK defence source told the BBC extra troops could be sent to Afghanistan, where six troops have died in a month.
The BBC's source said a request for more troops was being passed up the chain of command but had yet to reach ministers.
Answering a question from Conservative leader David Cameron, the prime minister told the Commons he had received no request for equipment or troops but they would get what they need.
He added: "They are fighting a battle that I think is important not just for the security of Afghanistan. It is important for the security of the wider world.
"It is absolutely right we give them every support. We will do that."
BBC correspondent in Kabul, Alastair Leithead, said the political debate meant commanders would be given a "blank cheque" to meet their needs in the field.
The soldier killed on Wednesday has not yet been named.
He was taking part in a foot patrol in Sangin town, in the troubled southern province of Helmand, at 1130 BST when his unit came under attack from Taliban forces.
There followed a firefight in which he was killed.
A statement from the Ministry of Defence said: "We can confirm that during a patrol in Sangin town, members of 3 Para battle group were attacked by suspected Taleban forces.
"It is with deep regret we can confirm that during the incident a British soldier has been killed."
His death follows the loss of two British servicemen in Helmand at the weekend.
Meanwhile, US-led forces in Afghanistan said they had killed about 35 militants in a raid on a "known Taleban compound" in Helmand.
The raid took place on Tuesday night in the village of Gujdar, some 25km (16 miles) east of Musa Qala in the south of the province.
On Wednesday, Afghanistan's capital Kabul was hit by blasts for a second day - one person died and at least 40 were wounded in three bombings targeted at buses carrying Afghan army officers and government workers.