In a move likely to sharpen concern that America may be planning military action against Tehran, Admiral William Fallon, head of central command, quit with immediate effect.

Last night he denied he was out of step with the White House, but said the "embarrassment" from the article made it impossible to do his job.

Robert Gate, the defence secretary, denied there was a rift with the admiral, but said: "I believe it was the right thing to do, even though I do not believe there are in fact significant differences between his views and administration policy."

Admiral Fallon was the subject of an article in Esquire magazine that portrayed him as opposed to President George Bush's Iran policy. It described him as a lone voice against taking military action to stop the Iranian nuclear programme.