As details begin to emerge of the blast which is feared to have killed six UK soldiers - including one thought to be from Calderdale - tributes are being paid.
Until the bodies can be recovered and formally identified, their deaths cannot be confirmed.
It is understood there were two Warriors vehicles travelling in a mounted patrol when the first vehicle was hit.
Prime Minister David Cameron has said today was a “desperately sad day”.
“This is a desperately sad day for our country and desperately sad of course for the families concerned. It is a reminder of the huge price that we are paying for the work we’re doing in Afghanistan, the sacrifice that our troops have made and continue to make. I do believe it’s important work for our national security, right here at home but of course this work we’re increasingly be carried out by Afghanistan soldiers and we all want to see that transition take place.”
At the start of Prime Minister’s Questions, he told the House of Commons.
“Our thoughts are with the family and friends of those brave servicemen.
“Every death and injury reminds us of the enormous cost paid by the armed forces to keep our country safe.”
He said the deaths would take the death toll of British soldiers in Afghanistan to more than 400.
Secretary of State for Defence, Philip Hammond, said: “This tragic incident brings home to us the dangers that are faced on a daily basis by the men and women of our Armed Forces deployed in Afghanistan. My thoughts are with the families and friends of the six soldiers who are missing, believed killed, and also with their colleagues, both in Afghanistan and the UK, whose brave work continues or is about to start.
If the deaths are confirmed it would be the biggest single loss of life in one incident since 14 people died in a Nimrod crash in 2006.