British troops aim to help stabilise the country
The UK is deploying 1,400 more troops to Afghanistan, Defence Secretary Des Browne has told MPs.
How many British troops are there in Afghanistan?
There are currently about 5,500 in the country.
Mr Browne had already announced a separate increase in troops, on 1 February, for southern Afghanistan, with a total number of 6,300 expected to be there by April.
The majority of troops involved in the latest announcement will be deployed mainly across the south over the summer, bringing the total number to 7,700, although numbers do fluctuate.
Where are they stationed?
The bulk of British troops - about 5,000 - are in the southern province of Helmand. This number will rise to about 5,800 by April.
There are also currently about 500 personnel at the Nato-led International Security Assistance Force (Isaf) headquarters in the capital, Kabul.
Why are they there?
They are there to help train Afghan security forces, facilitate reconstruction, and provide security.
In Helmand, the emphasis is also on counter-narcotics, as the province is the largest single source of opium in Afghanistan.
Helmand is the 'largest single source of opium' in Afghanistan
As 90% of the world's heroin comes from Afghanistan, the military regards hitting the trade at its source as key.
But the situation in the north of Helmand turned increasingly violent towards the end of 2006.
The BBC's Alastair Leithead, in Kabul, says the troops have been involved in clashes on a "daily basis" throughout the winter.
They are fighting against the Taleban and anti-coalition militia (ACM).
Troops have been involved in clashes in the towns of Sangin, Musa Qaleh, Kajaki and Nawzad.
The level of Taleban resistance has been significant, but British military officials insist they have won every clash.
Are British troops operating alone?
No, they are part of the Nato-led Isaf force, which is a United Nations-mandated organisation.
The three-year mission will cost £1bn
Nato took over command and co-ordination of Isaf in August 2003.
The Isaf mission is currently under the control of General Dan McNeill, from the US army. He succeeded Gen David Richards from the British army in February.
There are currently about 31,000 Isaf troops in Afghanistan.
These are being backed by about 30,000 Afghan troops and a similar number of Afghan policemen - all of whom are described as "fully equipped and trained" by the MoD.
What areas does Nato control?
Nato has troops across Afghanistan.
It took over total control of Afghan security in the eastern provinces, which had been under the control of US, in October 2006.
Prior to that, Isaf already commanded troops in the north, west and south of Afghanistan, as well as Kabul.
Nato's expanded role brought 14 provinces under its control.
The 37-nation Isaf said the US would retain control of some 8,000 of its troops for their "counter-terrorism" role and for training Afghan police and soldiers.
How much influence does the Taleban have in Helmand?
There are reported to be several hundred Taleban fighters in the area and it is thought there has been plenty of recruiting going on among the local population.
This is primarily done among disaffected youths or through paying people to join.
One explanation is that people feel the Afghan government has not offered them enough help or security.
Another factor is that the conservative views held in southern Afghanistan are in line with what motivated the Taleban - which was formed in that region.
Which units are involved?
In February 2006, an advance party of 850 personnel from 39 Regiment, Royal Engineers and 42 Commando, Royal Marines, with three Chinook helicopters, went to the southern province of Helmand.
Units from the 16th Air Assault Brigade, including the 3rd Battalion of the Parachute Regiment, headed the next deployment.
They were replaced in October 2006 by Royal Marines from the 3 Commando Brigade.
British forces are supported by Apache attack helicopters, Lynx light helicopters, Chinook support helicopters, Scimitar and Spartan armoured vehicles and a battery of 105mm light guns.
Hundreds of Royal Engineers are working on local infrastructure projects in Helmand, protected by Royal Marines and other soldiers.
There are also several RAF squadrons based in Kandahar and a number of Signallers based in Kabul.