Six UK soldiers have been reported missing presumed dead in southern Afghanistan, the Ministry of Defence has said.
Five soldiers belonging to the 3rd Battalion the Yorkshire Regiment and a sixth from the 1st Battalion The Duke of Lancaster's Regiment were on patrol when their vehicle was caught in an explosion.
The soldier's families have been informed.
Lt Col Gordon Mackenzie, spokesman for Task Force Helmand, said: "I have the tragic duty to report that six soldiers are missing, believed killed, during a security patrol.
"The six soldiers were on patrol in a Warrior armoured fighting vehicle when it was caught in an explosion in the Task Force Helmand area of operations."
Prime Minister David Cameron said it was a "desperately sad" day for the British armed forces as six British soldiers were missing and believed to have been killed after their armoured vehicle was hit by an explosion while they were on patrol in the Helmand area of southern Afghanistan.
"It is a reminder of the huge price that we're paying for the work we're doing in Afghanistan, the sacrifice that our troops have made and continued to make. I do believe that 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," he said.
The incident would also be the biggest single loss of life to enemy action in both the Iraq and Afghanistan wars. It also takes the number of those killed in Afghanistan since the start of operations in October 2001 past 400.