Defence Secretary Des Browne acknowledged that nothing could compensate for any individual loss, but said he remained convinced the campaign was "the noble cause of the 21st Century".
"We are making significant progress in Afghanistan. It's slow, sometimes it's frustratingly slow," he told BBC Radio 4's Today programme.
"The reason we are making that progress is because those very brave and professional young men and women have gone about their job in such a way that they have created, in the most difficult of circumstances, a degree of security that many people a couple of years ago thought was impossible."
Brig Mark Carleton-Smith, commander of British forces in Helmand Province, said Sunday's foot patrol had been returning to base through some villages when it was attacked by a single suicide bomber.
One other soldier was injured and was expected to make a good recovery, the Ministry of Defence said.
Brig Carleton-Smith said by resorting to suicide tactics, the Taleban were demonstrating that they no longer enjoyed support amongst ordinary Afghans.
Major Aidan Coogan, from the Parachute Regiment, said the deaths would be a "blow" to the dead men's colleagues but "would not affect their mission or their morale".
"Indeed, it will make them more determined to continue with the good progress that has been made in Afghanistan," he said.
The Chief of the Defence Staff, Air Chief Marshal Sir Jock Stirrup, said he reflected on the most recent deaths with "both a sense of deep sadness and pride" as the military effort was starting to achieve real change.
The soldiers are paying with their lives and their wounds to buy time for the political and the developmental process to take place
Prof Michael Clarke, Royal United Services Institute
Mr Browne told Today that he broadly agreed with the assessment of the director of the Royal United Services Institute Professor Michael Clarke about the current situation in the country.
The professor told the programme the military had done the best they could do under the circumstances, which was to establish a "stalemate" with the Taleban.
He added: "The soldiers are paying with their lives and their wounds to buy time for the political and the developmental process to take place. The problem is it hasn't taken place nearly fast enough."
Prof Clarke added the point at which Nato troops could "declare victory and leave" would be when they could genuinely say that whatever happened next was in the hands of the Afghan people
The parents of Captain David Hicks, killed in August 2007, remember their son
"That point is probably quite some years away," he added.
Mr Browne said the insurgency could not be won by military means alone, and that governance, economic development and a "battle for the people" were equally important.
Conservative party leader David Cameron said the country owed "so much" to the servicemen and women fighting in Afghanistan, with the death toll serving as a "tragic reminder of how brave and courageous they are".
Liberal Democrat leader Nick Clegg said that the cause for which the soldiers died was "a just one."
He added: "The consequences of failure in Afghanistan would be unimaginable - a boost to terrorists who seek to harm our way of life, an increase in hard drugs on our streets and terrible instability in an already unstable region."
Of the those killed in the country since 2001, 74 have died as a result of hostile action.
The remaining deaths were caused by illness, accidents and non-combat injuries, or else their causes have yet to be formally classified.
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