An Afghan soldier has killed three British troops during a joint patrol in the country's southern province of Helmand, a provincial security official has said.
Two more British soldiers were injured in the attack, which took place near Lashkar Gah, the provincial capital of Helmand, where some 9,000 British troops are based as part of the US-led forces, a security source told Reuters on Tuesday.
Meanwhile, NATO released a statement saying that three of its soldiers were killed in an attack by militants in southern Afghanistan.
Their deaths bring to 36 the number of foreign soldiers killed so far this month in Afghanistan.
American and NATO military casualties are on the rise as they step up attacks against Taliban strongholds in southern Afghanistan.
Britain has about 10,000 boots on the ground in Afghanistan, the largest international force after the United States. The UK says it is going to withdraw all its troops from Afghan combat zones by 2015.
The British government is under fire at home over the rising number of casualties in Afghanistan. Opinion polls show that most Britons want their troops back home.