A man wearing Afghan police uniform shot dead three British soldiers at a checkpoint in Afghanistan on Sunday, Britain’s Defence Ministry said on Monday.

The soldiers were serving with an Afghan police advisory team and were killed after a meeting at the checkpoint at Nahr-e-Saraj in southern Helmand province.

The assailant was injured and detained, a Defence Ministry spokesman said.

Their deaths take to 422 the number of British military personnel killed in Afghanistan since operations began in 2001.

NATO-led forces have suffered a string of attacks by members of Afghanistan’s security services on foreign troops and their mentors, adding to pressure on some countries to withdraw.

Britain has about 9,500 troops in Afghanistan and is due to withdraw 500 by the end of the year. It plans to bring home all its combat troops by the end of 2014.

Two of the soldiers killed on Sunday were from the 1st Battalion Welsh Guards and one was with the Royal Corps of Signals.