He replaces Admiral William Fallon, who resigned in March after saying that media reports describing him as at odds with the White House over how to deal with Iran had become "a distraction".

Before he leaves his current post, Petraeus will make a recommendation in mid-September on whether a recent reduction of US forces can continue after the last brigade of "surge" troops leaves Iraq in July.

In March, Robert Gates, the US defence secretary, said the long lead time into Petraeus's new role at Centcom and Odierno's takeover of the Iraq job were intended to avoid disrupting the "surge" strategy.