A British soldier has been killed and five others injured in a gun attack in northern Afghanistan, the Ministry of Defence has confirmed.
British soldiers stand guard near their damaged vehicle
The troops came under fire as they travelled between bases in the city of Mazar-e-Sharif, said the MoD.
Mazar-e-Sharif is the base for some 200 of the 1,000 British troops in the Nato-led peace force in Afghanistan.
The dead soldier was from the Royal Gloucestershire, Berkshire and
Wiltshire Light Infantry.
Announcing its "deep regret", the MoD said next of kin were being informed.
More details would be released in due course, said the spokesman.
He said there would be an investigation into who had shot at the troops.
"We are treating it as a hostile incident rather than friendly fire," he confirmed.
The MoD said security forces had sealed off the area in which the troops were attacked and arrested one suspect.
A spokesman said the troops had been travelling from the Provincial Reconstruction Team (PRT) base which houses international military and civilian personnel helping the Afghan government develop democratic institutions and disarming militias.
The British-led PRT has been operating in Mazar-e-Sharif since July 2003, with responsibility for five of the northern provinces.
Defence Secretary John Reid said: "My thoughts and sympathies are with the family and friends of the soldier tragically killed today in Mazar-e-Sharif."
The injured soldiers are being treated by German medics in nearby Kunduz, said to the MoD.
The Royal Gloucestershire, Berkshire and Wiltshire Light Infantry is the main British regiment operating in the area is , although soldiers from other units are also attached.
A spate of violent attacks linked to militants has been widespread in Afghanistan since March, and has killed more than 1,000 people.
The UK takes command of Nato's 12,000 peacekeepers, stationed mainly in the more stable north and west, in May.
But as many as 4,000 British troops - backed by assault helicopters - will be sent to southern Afghanistan in the coming months.