Several Americans who were held said they recognised the ultraconservative Ahmadinejad as a ringleader. But two Iranians who were leading figures in the storming of the embassy said he did not take part.

Bush said he did not know whether Ahmadinejad was involved and officials were analysing photographs and other information in what they said was a government-wide effort to get answers.

"Obviously his involvement raises many questions, and knowing how active people are at finding answers to questions, I'm confident they will be found," Bush told reporters.