The UK is to send another Royal Air Force fighter jet to Afghanistan, Defence Secretary Des Browne has said.
UK troops are coming under sustained attack
The move is a response to a "surge" in demand for close air support from British and other international troops fighting the Taleban, said a statement.
It brings to seven the number of British Harriers in Afghanistan. They are based at the Kandahar airfield.
It was intended to be a temporary deployment "kept under constant review", said Mr Browne.
British troops, as part of the Nato-led International Security Assistance Force, have been battling Taleban fighters in southern Afghanistan after taking over from a US-led coalition in July.
About 4,000 UK troops are in Helmand.
The area is where most of Afghanistan's opium production is concentrated, and sees regular deadly violence blamed on Taleban fighters or drug lords.
The total number of UK troops killed while on operations in Afghanistan since 2001 now stands at 40.
BBC correspondent Alistair Leithead, in Kabul, said unlike in Iraq, troops in Afghanistan were actually "standing up and fighting and getting through tens of thousands of rounds with heavy machine guns".
"It is very intense, very dangerous, and obviously very stressful for those people involved in it, given the difficulties of the terrain and the intensity of the fighting," said our correspondent.