Robert Gates, US defence secretary, has warned that American public opinion and the military itself have no appetite for a “long slog” in Afghanistan, in one of the frankest admissions yet from a top administration official of limited US patience in the war against the Taliban.

Mr Gates’ comments came amid concerns voiced by US legislators about current international strategy and continuing casualties on the front itself, with intensified fighting making July the deadliest month for western forces since the US-led invasion of 2001.