Canada has warned the US government that a narrow interpretation of new energy legislation would prohibit its neighbour buying fuel from Alberta’s vast oil sands, with “unintended consequences for both countries”.

In a letter to Robert Gates, US defence secretary, Canada said that it “would not want to see an expansive interpretation” of the Energy Independence and Security Act 2007. A copy of the letter, from Michael Wilson, Canadian ambassador, and copied to Condoleezza Rice, US secretary of state, and Samuel Bodman, US energy secretary, has been obtained by the Financial Times.