The British Defence Secretary, Des Browne, has admitted that Britain and its NATO allies seriously underestimated the resistance they were facing from Taliban fighters in Afghanistan.

In a speech to the Royal United Services Institute in London, Mr Browne said the Taliban had proved to be a more determined foe than expected.

Yesterday, four NATO soldiers were killed in Afghanistan in a suicide bomb attack by suspected Taliban militants. The blast targeted a Canadian patrol.

Over 90 foreign troops have been killed in Afghanistan this year following a surge in Taliban-related violence.

NATO forces, including 2,300 Canadian troops, took control of operations in southern Afghanistan from US-led forces on 31 July.