The US government had been bracing for scenes like the ones seen since the attacks on its diplomatic missions in Egypt and Libya on Tuesday evening.
On Friday, the protests spread after mid-day prayers in the Middle East, North Africa and across the Muslim world.
US embassies and other symbols of American influence have become focal points for violent demonstrations, leaving hundreds injured.
"There are frustrations, many [negative] perceptions about the US and the movie is nurturing this. It's very important for [Muslim] politicians, intellectuals, scholars to come out and say 'this [protests] is anti-Islamic, this is not the way to deal with this', and to come with the deep education about how to react to such provocations."
- Tariq Ramadan, a professor of Islamic studies
The Pentagon sent US marines to the Yemeni capital, Sanaa, as protests there continued.
Barack Obama, the US president, was at Andrews Air Force Base outside Washington DC as the bodies of Chris Stevens, who served as US ambassador to Libya, and three co-workers arrived after Tuesday's deadly consulate attack in Benghazi.
Obama said: "We will do everything in our power to protect Americans serving overseas…making it clear that justice will come for those who harm Americans…in our grief we will be resolute."
As for the 14-minute film trailer that apparently triggered the protests, little is known for sure. It is not even clear if a full-length film exists at all.
Jay Carney, a White House spokesperson, said: "This is a fairly volatile situation and it is in response not to United States policy, not to obviously the administration, not to the American people. It is in response to a video, a film that we have judged to be reprehensible and disgusting."
Earlier Al Jazeera asked Rashad Hussain, the US president's special envoy to the Organisation of Islamic Cooperation, if he thought the film was being used to stir up long-standing grievances against US foreign policy.
"We can't go through this every single time somebody does something offensive. We had the episode of Terry Jones, there [have] been other episodes and certainly it's not been limited to speech about Islam, it's about other religions as well, and it's important that we react to this hateful and offensive speech with better speech through efforts that address the underlying causes of intolerance…
"This is not about Salafis or unreformed security services…the bigger issue is public opinion in the Muslim world is not that radically different today than five years ago but what matters today is in countries touched by the Arab Spring and other Muslim countries is public opinion matters more."
- Flynt Leverett, a former senior US government official
"As a American Muslim I know the place of the prophet in Islam and the anger and sadness it causes people when there is an offensive video or depiction produced, now that doesn't in any way excuse violence. It's important that people understand that it's a sign of strength, not weakness, to refrain from violence," Hussain said.
The US has condemned the anti-Islam film along with the filmmakers. It has also tightened security at its diplomatic facilities around the world.
Demonstrations over the 14-minute trailer on Youtube of an anti-Islam film called Innocence of Muslims spread across the Muslim world with huge protests in Tunisia, Egypt, Libya, Sudan, Afghanistan, Yemen, Syria, Morocco, Bangladesh and Australia.
In this episode Inside Story Americas asks: What is really behind these protests?
Joining the discussion with presenter Shihab Rattansi are guests: Flynt Leverett, a former senior US government official; Michelle Dunn, a former US state department official; and Tariq Ramadan, a professor of contemporary Islamic studies at Oxford University, and the author of Islam and the Arab Awakening.
"In all of this the element of opposition to US policies is probably the least. This is very much parallel to the Danish cartoon [controversy] a few years ago…was that fuelled by an underlying hatred of Danish foreign policy in the Middle East? It was the specific perceived offense to Islam, and [in this case] along with the Salafi element, which is very important, especially in Egypt."
Michelle Dunn, a former US state department official
ABOUT THE INNOCENCE OF MUSLIMS FILM:
- Questions have been raised over the identities and motives of the film's makers
- The poorly-made, low-budget film was only shown in a theatre once
- The actors in the film say they were duped about the nature of the film. They say the anti-Islam rhetoric was dubbed in during post-production. They thought the movie was about life in the Middle East 2,000 years ago
- For most Muslims, any depiction of Prophet Muhammad is blasphemous
- The filmmakers are reportedly associated with Christian extremists in California
- Initial reports say the filmmaker was Sam Bacile but this was proved untrue
- According to US officials an Egyptian Copt named Nakoula Basseley Nakoula made the film. Nakoula was convicted of bank fraud in California in 2009. US officials suspect Nakoula used 'Sam Bacile' as a pseudonym
- The filmmaker claimed the video was made with money from Jewish donors. He also claimed to be an Israeli Jew but Israel had no record of him
- The 'consultant' for the film, Steve Klein, is an anti-Muslim activist in California. Civil rights groups say Klein trained militant Christian groups
- Terry Jones, the Quran-burning US pastor, was involved in promoting the film