Britain's Foreign Office says its ambassador to Iran has rebuked the country's vice president for calling British people idiots.
In a speech on Monday, Mohammad Reza Rahimi said Britons were "a bunch of idiots ruled by mafia," and criticized Prime Minister David Cameron's inexperience.
Though British officials usually let such remarks pass, Ambassador Simon Gass wrote a blog posting in Farsi on a government Website sharply criticizing Rahimi.
He said the Iranian official had shown a lack of respect with his "illogical and worthless remark."
The Foreign Office says it decided Rahimi's comments merited a response.
Britain is one of six nations negotiating with Tehran over its disputed nuclear program. Iran denies it is developing nuclear weapons.