Six British soldiers have been killed after an explosion hit their armoured vehicle in southwestern Afghanistan.

Afghan National Army soldiers take position near the site of a blast in Helmand province, March 7, 2012.

The soldiers were on patrol in Helmand province at the time of the blast on Tuesday evening. The attack is suspected of being carried out by Taliban militants.

Britain's defence secretary Philip Hammond said efforts were under way to recover the vehicle and identify the soldiers. He added that Tuesday's attack would not derail the country's mission.

It's the biggest loss of life for British forces in the country since a plane crash in 2006. The deaths are expected to fuel calls for the acceleration of a planned withdrawal of all US-led coalition troops from Afghanistan by the end of 2014.

The attack brings Britain's overall military death toll to 404 since the war began back in 2001.