A suicide bomber rammed a vehicle packed with explosives into a British Embassy vehicle in the Afghan capital Kabul, killing at least five people including a British security guard.
An Afghan national who was driving the vehicle was also killed and a second British security guard was injured, Foreign Secretary Philip Hammond said in a statement.
Afghanistan's Interior Ministry spokesman Seddiq Sediqqi confirmed four Afghans were killed in the attack and another 33 civilians were injured.
Afghan police said a vehicle packed with explosives rammed the heavily-armoured embassy vehicle, exploding on impact and sending a huge plume of dust and smoke into the air.
The mid-morning attack happened on the traffic-choked road between Kabul and Jalalabad city. Witnesses said at least a dozen civilian cars were damaged by the blast, and the road was strewn with smouldering debris from the British vehicle.
Video footage showed the roof of the embassy vehicle had been blown off and flung about 50ft along the road, an indication that it was a powerful blast as the vehicles are built to withstand substantial impact.
Taliban insurgents claimed responsibility for the attack in a brief statement.
The area of the blast in eastern Kabul has many foreign compounds and international military installations. In recent weeks, suicide bombers have launched attacks on military convoys in the area and on compounds housing foreign service companies and their international employees.
Today's attack was the first on a diplomatic target in Kabul for some time.