Crowds of angry, mainly Muslim, protesters gathered before the US Embassy in Cairo on Wednesday evening to denounce a short film – produced by a US-Israeli filmmaker – that critics say defames Islam and the Prophet Mohammed.

In the dim light, a couple hundred protesters chanted against the US and repeated pro-Islam slogans. "God is Great," they shouted. "We heed your call, oh Prophet of God."

Separated from the walls of the US embassy by lines of Egyptian policemen and armoured cars protecting the diplomatic mission in downtown Cairo, protesters voiced rage that someone had dared to produce a film that they perceive as defaming their prophet and that no officials had formally apologised for the movie.

"I'm here to voice my displeasure with the defamation of this sacred person, the Prophet Mohammed," said 29-year-old protester Maha Ahmed.

Demonstrators demanded an apology from the US government, saying that if no such apology was forthcoming by Friday they would stage an open-ended sit-in. On Friday, members of the Muslim Brotherhood, Salafist parties and others are planning a million-man rally in Cairo's Tahrir Square to register their anger.

When asked, most protesters said they did not belong to any particular political group, stressing that no one had asked them to come to the protest. Protesters were mainly male; only very few women could be seen among the demonstrators.

Most men sported long beards, while the few female protesters wore veils.

Protesters said that police personnel were very friendly with them, neither violent nor aggressive as they had been during the era of ousted president Hosni Mubarak.

"They let us protest and take down the American flag from the embassy," Ali Hafez, a member of the 'Trustees of the Revolution Assembly' told Ahram Online. "These changes are a result of the new administration of [Islamist President] Mohamed Morsi."

Unlike Tuesday's protest, Coptic-Christian demonstrators could not be spotted at the scene. The first day of the protest had featured members of Coptic organisations, such as activist group Maspero Copts United, who protested to register their rejection of religious defamation.

"We took part in the protests since we know what it's like to suffer from insults to our religion; we can relate to how the Muslims feel now," Hani Ramsis, a leading member of Maspero Copts United, told Ahram Online via phone.

Initially, the film was thought to have been made by US-based Coptic-Christian activists, but was later found to have been produced by US-Israeli dual-national filmmaker Sam Bacile. The false news about Coptic involvement in the film was initially spread by some local news agencies.

In response, protester Abu Islam Abdulla, owner of the Islamist-oriented Al-Umma television channel, set fire to a Christian Bible in the middle of the protest, according to an eyewitness at the scene and a video that appeared online. While some protesters appeared to welcome the contentious act, others appeared to voice disapproval, say witnesses.

"But why not burn the Bible when they approve of burning our Quran?" the woman protester told Ahram Online.

A number of protesters condemned the notion of burning Bibles, pointing to Islamic proscriptions against defaming Jewish and Christian symbols.

The film was promoted by Maurice Sadek, a controversial Coptic figure living in the US, along with Pastor Terry Jones, a firebrand American Christian preacher known for organising mass burnings of Muslim holy book the Quran.

The incident appears to have prompted resentment towards Egypt's Coptic-Christian community.

"Several Facebook groups are warning us about possible attacks and murder," Ramsis said. "What did we do deserve this?"

Some protesters attributed the film to Zionist groups, which, they say, want to degrade Islam and sow sectarian division between Egypt's Christians and Muslims.

"We tell these Zionists: you aren’t capable of making war with God," Ahmed Mubarak, a lawyer and Islamic Law expert, told Ahram Online.

The protests against the controversial film coincided with the eleventh anniversary of the 9/11 attacks in New York and Washington. A similar protest outside the US consulate in Benghazi left four American officials dead, including the US ambassador to Libya.

Many Egyptian political groups and figures condemned the film, while others denounced the violent reactions in Libya.

Tarek El-Zomor, spokesman for Egypt's Gamaa Islamiya movement, for his part, censured Tuesday's protest at the US embassy in Cairo, denying that any Islamist groups – or their respective youth wings – had taken part in it. El-Zomor went on to describe the removal of the embassy flag as "illegal and against Islamic Law," but praised the Cairo protest's peaceful nature. 

Egypt's Democratic Front Party, for its part, criticised the North America-based group Expatriate Copts, holding it responsible for the offensive film and accusing it of trying to stir strife between Muslims and Christians in Egypt.

The party went on to urge President Morsi to postpone his scheduled US visit, slated for 24 September, to register Egypt's objection to the film.

Islam forbids the depiction of the Prophet Mohammed in any manner. A Danish newspaper's publication of 12 caricatures of the prophet in 2005 sparked riots in several Muslim countries.