The leader of the British army in Afghanistan has said more troops are likely to be killed in the battle against Taleban forces.
Helmand is one of Afghanistan's toughest areas
Brigadier Ed Butler was speaking after two British soldiers died during operations in Helmand province.
They were killed on Saturday in an attack on the regional headquarters in the town of Sangin.
Both men served with the 3rd Para Battlegroup. Four other soldiers were injured in the attack.
The British outpost was targeted by fighters with light weapons and rocket-propelled grenades.
Following the soldiers' deaths, coalition air-strikes targeted a suspected Taleban hide-out in the Joshali area of Sangin, killing at least nine militants.
Five British soldiers have now been killed in Afghanistan in the last three weeks. Most of the 3,300 British troops in the country are in Helmand.
'Facing down the Taleban'
Brigadier Butler said: "Of course any casualties are hugely regrettable, and we feel for the families of those soldiers."
But he added: "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."
He warned more soldiers would be injured, or even killed, as forces try to impose order on the lawless south of Afghanistan.
But he rejected comparisons with the situation in Iraq, saying: "They are two different missions".
Army chiefs have now got to decide how to react to events in Helmand, according to Alastair Leithead, BBC correspondent in Kabul, who said the latest deaths were a "severe blow".
"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."
British soldiers have been taking a "soft hat" approach, wearing berets instead of helmets whilst on patrol and are still trying to win Afghan "hearts and minds".
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."
But Major General Patrick Cordingley, who led British forces in the first Gulf War, said more soldiers may be needed to bolster the 3,300 already in Afghanistan.
Major Cordingley, who recently visited Helmand, said: "We mustn't be humiliated at this stage.
"We have got to actually crack on with this thing and, however sad it is, we have got to push forward and make sure we establish our presence there."
Labour MP Mike Gapes, chairman of the foreign affairs committee, told BBC Breakfast: "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."
Shadow foreign secretary William Hague said British troops were effectively "at war" in Afghanistan.
He said they were being asked to win the hearts and minds of the Afghan people while removing their main source of income.
Mr Hague said that, unless the British could demonstrate an alternative future to growing opium and being with the Taleban, they would not succeed.
The cross-party Commons Foreign Affairs Committee also warned that there was a "fundamental tension" at the heart of the Afghanistan mission which could make the security situation worse by flushing out drug barons.