Six British soldiers have been killed in an explosion in Helmand province in southern Afghanistan, taking the British toll to 404 since the 2001 US-led invasion to oust the Taliban.
The soldiers, five from the 3rd Battalion the Yorkshire Regiment and one from the 1st Battalion The Duke of Lancaster's Regiment, were on patrol when their Warrior Armoured Fighting Vehicle was struck, the British Ministry of Defence said.
Mohammad Ismail Hotak, a senior Afghan police official in Helmand, said the explosion was caused by a roadside bomb.
It marks the biggest single loss of life for British troops in Afghanistan since 2006.
"It is a reminder of the huge price that we are paying for the work we are doing in Afghanistan and the sacrifice that our troops have made and continue to make," British Prime Minister David Cameron told the BBC.
"I do believe it's important work for our national security right here at home but of course this work will increasingly be carried out by Afghan soldiers and we all want to see that transition take place."
Foreign combat troops are due to leave Afghanistan at the end of 2014.
Doubts persist about the ability of Afghan soldiers and police to control one of the world's most unstable countries.
Britain has some 9,500 soldiers in Afghanistan, a number due to be reduced in phases as it ends combat operations in the next two years.
