Egyptian troops have opened fire on supporters of ousted President Mohammed Morsi marching in Cairo, killing three people and wounding dozens.

The shooting came as crowds moved on the Republican Guard headquarters, where Mr Morsi is believed to be held.

BBC correspondent Jeremy Bowen said the military had told demonstrators to stay back from the officers' club at the Presidential Guard building.

When the crowd surged forward, "I saw barrels of guns lowered and shooting into the crowd... very shortly after that there was a man dead on the ground."