The British man killed in a Taliban attack in Kabul has been named as 33-year-old Luke Griffin.
The Merseyside local was killed alongside four Afghanistan nationals, who also worked for G4S, in the suicide attack on a compound on Wednesday.
Charlie Burbridge, managing director of G4S Risk Management Group, confirmed the deaths "with great sadness".
Thirty-two employees were also injured, five seriously after a Taliban suicide bomber rammed an explosive-packed truck into the gate of the G4S compound in eastern Kabul.
The blast was so strong it caused a crater at the scene.
Insurgents armed with grenades and automatic rifles then proceeded to storm the building, engaging in a drawn out battle with Afghan forces.
Charlie Burbridge said: "Next of kin have been informed and our thoughts at this difficult time are with the loved ones of those who have died and been injured, and our brave team in Afghanistan who have lost colleagues and friends. We are offering support and counselling to all of those affected."
It is understood that G4S have been providing security in Afghanistan to a number of bodies including non-governmental organisations and corporate clients since 2003.
Zabihullah Mujahid, a spokesman for the Taliban, claimed responsibility for the attack in a statement posted on Twitter.
The group has since said it was launched in revenge for a US airstrike which was carried out hours before in southern Afghanistan that killed 30 people - including civilians, as well as children.
The Taliban carry out near-daily attacks on Afghan security forces, and the one in Kabul came hours after officials said at least 30 civilians were killed along with 16 Taliban fighters during a battle between government forces and insurgents in southern Helmand province.G4S provides training for Afghan security forces.