Two British soldiers have been killed in southern Afghanistan during operations in Helmand province.
More than 3,000 British soldiers are serving in Afghanistan
They were killed on Saturday when a rocket-propelled grenade struck one of the defensive posts at the regional headquarters in the town of Sangin.
Both soldiers were serving with the 3rd Para Battlegroup.
Five British soldiers have now been killed in the country in the last three weeks. Most of the 3,300 British troops in Afghanistan are in Helmand.
A Ministry of Defence spokesman said: "It is with deep regret that we can confirm that two British soldiers from the 3rd Para Battlegroup have been killed in action.
"Their next of kin are being informed."
Other soldiers are also thought to have been wounded in the attack but the military has declined to say how many.
Defence secretary Des Browne said: "My thoughts are with the family and friends of those killed in the attack against UK troops in Afghanistan.
"Our troops are in Afghanistan to help the Afghans rebuild their country. That means facing down the Taleban who will go to any lengths to oppose progress.
"In doing this job we lost two of our troops yesterday and I am greatly saddened by this."
BBC correspondent in Kabul, Alastair Leithead, said the latest deaths were a "severe blow" to the British military commanders in Afghanistan, who were now considering their options.
He said: "There are lots of heavy discussions going on at the moment to decide exactly what to do.
Helmand is one of Afghanistan's toughest areas
"To have such heavy losses in such a short period of time has obviously shaken the military command in southern Afghanistan.
"They knew it would be a very dangerous mission but they never wanted to be quite so exposed in such remote parts of Helmand province so early in their deployment.
"Whether they will send more troops in from their main bases in Helmand, or whether they will withdraw the troops are decisions which the commanders will make.
"But this will be a severe blow to the deployment and to their mission in Afghanistan."
Our correspondent says British soldiers are still taking a "soft hat" approach, wearing berets instead of helmets whilst on patrol and are still trying to win Afghan "hearts and minds".
Calls for statement
Labour MP Mike Gapes, chairman of the foreign affairs committee, told BBC Breakfast about his concerns at what he sees as a deteriorating security situation faced by British troops in Afghanistan.
He said: "Clearly British forces have just recently moved into this southern province of Helmand and as a result of that they're in a more dangerous environment.
"They're now taking on the resurgent Taleban and obviously they need to have sufficient force and they need to be protected properly in that area.
"I am concerned, yes, and I hope the government will be giving us a statement very soon on what they intend to do to deal with this situation, because clearly we need to make sure that our forces in Afghanistan get the full support that they need."
Patrick Mercer, Conservative security spokesman and a former infantry officer, told BBC Radio 4 the government had not committed enough combat force to the mission.
He said only 600 infantrymen and a battery of guns, with some helicopters, had been pledged to the region.
"When I was instructing at the staff college, if a student had presented me with this plan for Afghanistan, I would have failed him, and failed him comprehensively," he said.
The commander of British forces in Afghanistan, Brigadier Ed Butler, said he is prepared for further casualties in the battle against Taleban forces.
"Of course any casualties are hugely regrettable and we feel for the families of those soldiers," he said.
"Like the start of any operation, one anticipates casualties and we are prepared that there will be unfortunately more casualties, as we win the campaign against those people who oppose security, who oppose the government of Afghanistan and those who won't want this place to be a better place to live."
The Commons defence committee has previously said attempts to crackdown on the region's drugs barons could actually result in a deterioration in the security situation which the troops are supposed to stabilise.
MPs have also said they were "deeply concerned" that the military taskforce lacked sufficient close air support or transport helicopters.
They have called for the Ministry of Defence to produce evidence that the RAF's Hercules transport aircraft were fitted with adequate "defensive aids suites" to protect them from ground attack.
The British troops are in the country to help train Afghan security forces, facilitate reconstruction and provide security.
In Helmand the emphasis is also on counter-narcotics, as the province is the "largest single source of opium in Afghanistan".