Gordon Brown reacts to the deaths of two more British soldiers in Afghanistan
Gordon Brown has said the UK's commitment to Afghanistan is "undiminished" despite the death of a further two British soldiers in action.
Nine British personnel have died in the past nine days, leading to criticism of the UK's strategy in Afghanistan from the Lib Dems and Conservatives.
Lib Dem leader Nick Clegg said Mr Brown should "stop pretending that this is someone else's conflict".
Mr Brown said "success" in the mission would honour those who had died.
Speaking in Italy, where he is attending the G8 summit, Mr Brown spoke of his "sadness" at the loss of more lives after it was confirmed soldiers from the 4th Battalion The Rifles and the Princess of Wales's Royal Regiment had died.
The number of British service personnel killed in Afghanistan since 2001 has risen to 178.
Mr Brown praised the "incredible professionalism, courage, bravery and dedication" of British troops serving there.
It really does show how we have got to redouble our efforts to make sure everything we are doing is actually working
And he said the UK and its coalition partners were determined to see their mission through although he accepted the Afghan army and police must be strengthened.
"Our resolution to complete the work we have started in Afghanistan and Pakistan is undiminished," he said.
Speaking later, Defence Secretary Bob Ainsworth said he believed the fight against the Taliban was "winnable" but admitted this would not happen "in the short term".
British troops were in Afghanistan to protect its citizens from the insurgents, he said, and to "remove the threat" they posed to the UK's security.
On the issue of equipment, he said there had been a "massive improvement" on the front line but more could be done and risk could not be eliminated entirely.
The Lib Dems repeated their calls for the army to be given more helicopters in Afghanistan, saying the war must be fought "properly or not at all".
"We need to ask ourselves very simple, hard, tough questions," Nick Clegg said, adding the latest deaths had caused "immense distress".
"Are we giving them the backing they deserve? Are we giving them the troop numbers they need? Are we giving them the equipment that they must have to protect themselves from harm. Are we putting a political strategy in place to make sure their efforts are not in vain?"
In recent days, Mr Clegg has suggested the government turned down a request from the Army to send an additional 2,000 troops earlier this year ahead of next month's elections, limiting reinforcements to an extra 800.
Nick Clegg asked whether the forces were given the backing they deserved
Conservative leader David Cameron said the news of further UK casualties was "desperately sad".
They demonstrated the "very high price" that the Army was paying for its efforts in Afghanistan.
"It really does show how we have got to redouble our efforts to make sure everything we are doing is actually working."
He said the British public understood the need to stabilise Afghanistan to prevent the spread of terrorism but argued "some serious changes" in strategy were needed.
People wanted to see more done to equip the country for the future by building up its army, tackling corruption and the drugs trade, he said.
"It is vital we do that to make sure these lives are not lost in vain."
Ministers say they will do everything to ensure troops have the resources needed to do the job being asked of them.
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