Military officials said they were investigating the deaths amid conflicting reports of what had happened and "a very confusing picture on the ground".The Marine, from 40 Commando, and the soldier, understood to be a woman aged 25 from 3 Medical Regiment, were initially believed to have been shot dead by Taliban insurgents while on patrol in Nahr-e Saraj district.
However there were other reports they may have been killed by an Afghan policeman or soldier in an insider attack. Meanwhile, an Afghan police official said that the deaths were believed to have been caused by friendly fire when a British unit fired on another in a case of mistaken identity.
A spokesman for British troops in Helmand said the two "died from injuries sustained whilst on patrol in the Nahr-e Saraj district".
Their families have been informed.