Robert Gates, the US defence secretary, has warned that Nato risks becoming a “two-tier” alliance unless some members were willing to send more troops for the campaign to defeat the Taliban in Afghanistan.

”You have some allies willing to fight and die to protect peoples’ security, and others who are not. It puts a cloud over the future of the alliance, if this is to endure and perhaps even get worse,” Mr Gates told the Senate armed services committee on Wednesday. Mr Gates praised the Canadians, the British, the Australians, the Dutch and the Danes who were ”really over there on the line and fighting”. ”But there are a number of others that are not,” he added, in an apparent reference to countries such as Germany.