Clashes at the US embassy in Cairo erupted late Wednesday and continued till the morning of next day, as around 200 protesters and Central Security Forces (CFS) threw rocks back and forth.

Some of the demonstrators – most of whom are young and not bearded like many of the protesters who had participated in Tuesday's rally at the US mission – also hurled fire bombs at the CFS, who in return used tear gas in an attempt to disperse the crowd.

Earlier on Wednesday, crowds of angry, mainly Muslim, protesters gathered before the US embassy to denounce a short film, which critics say demeans Islam and the Prophet Mohammed.

It is not clear, however, what ignited the confrontations afterwards.

State-run news agency MENA reported that the protesters are from the football Ultras fan groups, who tried to "break into the headquarters of the embassy" but the CSF protected the premises against the attack. Backed by many armored vehicles, police have cordoned off the site. 

On Tuesday, Egyptian protesters took down the American flag from the walls of the US embassy as a thousands-strong demonstration held to condemn the film, which is reportedly produced by a California-based filmmaker called Sam Bacile. An AP report, however, indicates that Bacile may be a pseudonym for a Coptic-Christian living in California.

The Ultras White Knights – Zamalek Club's hardcore football fans – claimed that members of their group had brought down the US flag. While group members have since retreated from the scene, they say they are planning additional rallies to protest the film.

Yet the group categorically denied instigating violence on Wednesday.

"Our members are not present around the US embassy now. We stress that our participation in the demonstrations was peaceful, we just wanted to send a message (to authorities)," Ultras White Knights said in a statement on their Facebook page in the midst of the clashes by dawn.

"We condemn and reject the continuation of the same repressive and unfruitful tactics used by security forces in dealing with such situations." 

The battle on Wednesday, which lasted till after dawn, was moved away from the headquarters of the US embassy after the security personnel forced the frenzied crowd to move back towards the nearby Tahrir Square.

A police vehicle was reportedly set on fire.

Initial reports also said that several protesters were injured, most of whom suffered the effects of tear gas. An official injury toll has yet to be revealed.

The security forces, who according to MENA have arrested a number of protesters, also used loudspeakers to warn the demonstrators against approaching the now heavily-fortified embassy.

"We would sacrifice our blood and soul for the prophet," chanted protesters, most of whom did not carry banners or placards, every now and then during the clashes.

Demonstrators have demanded since Tuesday an apology from the US government for the film, saying that if no such apology was issued by Friday they would stage an open-ended sit-in.

On this Friday, members of the Muslim Brotherhood, Salafist parties and others are planning a million-man rally in Tahrir Square to vent their anger.