Egypt's interior minister has vowed to investigate the beating of a naked man by riot police that threatened to further inflame popular anger against security forces, but suggested that initial results absolve the police of direct abuse.

The beating was caught on camera by The Associated Press and the video was broadcast live on Egyptian television late on Friday as protests raged in the streets outside the presidential palace.

The AP video showed police trying to bundle the naked man into a police van after beating him.

Speaking to reporters after Friday's assault, Interior Minister Mohammed Ibrahim said initial results from the public prosecutor's investigation show that 48-year-old Hamada Saber was undressed by "rioters" during skirmishes between police and protesters.

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He was then hit in the foot by a bird shot, the minister said, stopping short of saying if the injury was a result of police firing into the crowds.

"The central security forces then found him lying on the ground and tried to put him in an armoured vehicle, though the way in which they did that was excessive," said Ibrahim.

A statement by President Mohammed Morsi's office called the incident "shocking", but stressed that violence and vandalism of government property is unacceptable.

In the latest twist, the victim has spoken from his hospital bed, saying army soldiers were in fact helping him after he had been attacked by protesters who mistook him for police.

Less than 24 hours after the incident, several thousand anti-government demonstrators marched again on the palace Saturday denouncing the police and Morsi after a week of violent protests that claimed more than 60 lives nationwide.

Source: Al Jazeera and agencies