US-led coalition and Afghan troops have embarked on the largest counter-insurgency operation since the fall of the Taliban to oust militants from their strongholds in southern Afghanistan.

Operation Mountain Thrust will involve more than 10,000 troops from Britain, Canada and the US as well as newly trained forces from the Afghan national army in a push against rebels who have become increasingly bold in the four southern provinces, said Lt Col Paul Fitzpatrick, the US military spokesman based in Bagram.