CAIRO, Egypt -- Egypt's Interior Minister vowed Saturday 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 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.

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

Speaking to reporters after Friday's assault, Interior Minister Mohammed Ibrahim said that 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. He was then hit in the foot by a bird shot, the interior 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.

In the AP footage from Friday, at least seven black-clad riot police beat Saber, whose pants are down around his ankles, with sticks before dragging him along the muddy pavement and tossing him into a police van.

The beating happened as thousands of protesters chanted against Morsi, throwing firebombs and firing flares at the presidential palace as police pumped volleys of tear gas and bird shot into the crowd, killing one protester and wounding more than 90.

The Interior Ministry said in a rare statement that it "regrets" the beating, and that it too is investigating the incident. But it also sought to distance itself -- and the police in general -- from the abuse, saying that "what took place was carried out by individuals that do not represent in any way the doctrine of all policemen who direct their efforts to protecting the security and stability of the nation and sacrifice their lives to protect civilians."

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

Ibrahim said nearly 400 policemen have been wounded this past week, warning that the disintegration of police will lead to even wider-spread chaos in the Arab world's most populous nation.

"The collapse of police will affect Egypt and transform it into a militia state like some neighbouring nations," Ibrahim said, eluding to Libya where militias comprise the bulk of security after that nation's uprising.

Already some Islamists have warned they could set up militias to protect their interests, while a group calling itself "Black Bloc" whose followers wear black masks claim to defend protesters opposed to the Islamist president's rule.

Ibrahim is the fifth interior minister to head the security force in the past two years. Distraught police officers heckled him earlier in the week when he showed up for the funeral of two officers killed last weekend, angry over attacks against them and investigations into their use of power after decades of near impunity under ousted leader Hosni Mubarak.

Rights groups have accused Morsi of not taking steps to reform the Interior Ministry, which was long the backbone of Mubarak's regime. Police under Mubarak were notorious for using excessive force against protesters and beating those in custody. The uprising against his rule erupted in early 2011 in large part out of anger against widespread police powers and impunity.

In a defining image of post-Mubarak violence against protesters, Egyptians were outraged last year when military police were caught on camera dragging a veiled woman through the streets during a protest, pulling her conservative black robe over her head and revealing her blue bra.

Protesters and rights groups have most recently accused police of using excessive force this past week during a wave of mass demonstrations in cities around the country called by opposition politicians, trying to wrest concessions from Morsi.

But many protesters go further, saying Morsi must be removed from office, accusing his Muslim Brotherhood of monopolizing power and failing to deal with the country's mounting woes. Many have been further angered by Morsi's praise of the security forces after the high death toll.

The chaos prompted Morsi to order a limited curfew in three provinces and the deployment of the military to the streets.

The main opposition National Salvation Front said Saturday that the "gruesome images" of Saber's beating requires the dismissal of the newly-appointed interior minister. The statement said that Ibrahim was sworn-in in early January, police have been using "excessive force" more frequently against protesters.

In an attempt to heap more political pressure on Morsi, the opposition said the assault comes as little surprise since the president called on the police to deal firmly with protesters, among them rioters.

Prime Minister Hisham Kandil said he visited Cairo's Tahrir Square and the area of the presidential palace Saturday, which were largely quiet after Friday's protests. He said those who are camped out there are neither protesters nor revolutionaries.

"Protesters do not torch, attack hotels, rape women, steal shops, they do not burn the presidential palace. These are not revolutionaries," he said.

In an impassioned speech Saturday carried live on Egyptian state TV, Kandil said the street violence and political unrest that has engulfed the country for more than a week is threatening the nation's already ailing economy.

"The Egyptian economy is bleeding," he said. "It is holding itself, but if this situation persists it will be dangerous, extremely dangerous. No government can govern a nation with this chaotic situation."

Foreign currency earners such as tourism and foreign investment have dried up in the past two years of political unrest. Foreign reserves currently estimate at around $15 billion, less than half of where it stood before the 2011 uprising that ousted Mubarak. The Egyptian pound has also lost around four per cent of its value due to the turmoil and planned austerity measures threaten to curb subsidies relied on by millions of poor Egyptians.

Kandil called on the opposition to back away from any more protests or marches.

"The world is watching to see how we will deal," he said. "It is upon all political parties to pull their peaceful protesters from the streets now."

Also Saturday, Mubarak's former interior minister, Habib al-Adly, was found guilty of abusing his position to force police conscripts to work on his mansion and land on the outskirts of Cairo. Both he and former riot police chief, Hassan Abdel-Hamid, were sentenced to three years in prison and fined around $340,000. The verdict can be appealed.

Al-Adly is already serving time for corruption and was sentenced to life in prison with Mubarak for failing to prevent the killing of nearly 900 protesters during the 2011 revolt that ousted the longtime leader. Both men appealed, and will be given a retrial.