Foreign Secretary David Miliband held talks with President Hamid Karzai on a surprise visit to Afghanistan Tuesday and met British troops in the fight against extremists, officials said.

Miliband, who arrived late Monday, met Karzai in the capital and then travelled to the southern province of Helmand with the Afghan Foreign Minister Rangin Dadfar Spanta, the British embassy in Kabul said.

Britain is the second-largest contributor of troops to the NATO-led International Security Assistance Force (ISAF) of nearly 51,000 soldiers that is helping the Afghan government fight a Taliban-led insurgency.

There are about 8,000 British soldiers in ISAF, most of them based in the opium-growing region of Helmand which is also a Taliban stronghold.

A British soldier was killed in an explosion in the province on Monday, taking the country''s death toll in Afghanistan to 126 since 2001, the year the Taliban were forced from government in a US-led invasion.

Helmand sees some of the worst of the Taliban''s insurgency and most of its districts are said to be in control of the rebels, despite the efforts of the British troops.

Karzai told a separate meeting Tuesday with a visiting delegation from the UN Security Council that it was "unacceptable" that districts were in Taliban control in places like Helmand, his spokesman Homayun Hamidzada said.