The Egyptian military has staged an apparent show of strength in the capital Cairo during a sixth day of anti-government protests.
Two air force jets and a helicopter are repeatedly flying low over Tahrir (Liberation) Square, the main gathering point for demonstrators.
A column of tanks arrived there only to have its path blocked by demonstrators.
Meanwhile, US Secretary of State Hillary Clinton has called for an “orderly transition” of power in Egypt.
“We want to see an orderly transition so that no-one fills a void, that there not be a void, that there be a well thought out plan that will bring about a democratic participatory government,” she told the Fox TV network.
“We also don’t want to see some takeover that would lead not to democracy but to oppression and the end of the aspirations of the Egyptian people.”
The BBC’s Jeremy Bowen, in Tahrir Square, says there is a mood of defiance among the anti-government protesters there, who are accusing the military of trying to intimidate them.
Earlier, despite the presence of armoured vehicles, the protesters appeared to have free rein in the city centre, with no sign of the riot police with whom they have clashed violently in recent days.
At one point, an army officer was carried aloft on the shoulders of cheering protesters.