A British soldier serving with the International Security Assistance Force (ISAF) in Afghanistan has been shot dead by a man in an Afghan army uniform, according to the US-led military coalition.In a statement released on Tuesday, ISAF said that the incident, which took place in southern Afghanistan on Monday, was "under investigation"."The British soldier was killed when a suspected Afghan soldier opened fire first at Afghan troops and then at British soldiers," said Major Martyn Crighton, an ISAF spokesman. "In the subsequent engagement, the attacker was killed by British troops."The attack took place in the Nahr-e-Saraj district of Helmand province, and the soldier was a member of the UK's engineering regiment in the area, the spokesman said.Ghulum Rasool Zazai said a joint commission of Afghan and NATO officers were investigating the assault, and attempting to determine whether the killer was a member of the Afghan National Army.The attack was the latest in a series of "insider" attacks, in which Afghan security forces, or people in Afghan security forces' uniforms, have killed more than 60 ISAF soldiers and trainers since the beginning of 2012.The incident happened as US President Barack Obama prepares to host Afghan President Hamid Karzai at the White House later in the week for talks focused on the long-term security agreement between the two countries.The threat of insider attacks has become so serious that international soldiers working alongside Afghan security forces are often looked over by so-called guardian angel troops on duty to provide protection.Foreign troops are not the only targets of such attacks, and the number of Afghan deaths in such incidents is estimated to be at least double the number of ISAF soldiers and trainers killed.There are currently about 100,000 US-led troops fighting alongside Afghan security forces against the Taliban and other groups.NATO combat forces are scheduled to withdraw from Afghanistan by the end of 2014.