Britain's increasingly heated debate about its role in Afghanistan has sparked concern in Washington about the sustainability of the military strategy and the US public's own willingness to commit troops for the long term, senior officials and analysts say.

The death of 15 British soldiers in two weeks has led to agonising in the UK over the Afghanistan war, with the military pushing for more troops in Helmand province, opposition parties calling for better equipment and the renewal of discussion about why the UK is taking part.