(CNN) -- The birthplace of the Arab Spring seethed Friday as anti-American rage sparked by an online film that insulted Islam's prophet boiled over across the Muslim world.
Hundreds of demonstrators turned out in Tunisia, the country where the self-immolation of a street vendor nearly two years ago set in motion widespread protests that toppled dictators in the region.
But Friday was an entirely different scene as protesters set their sights on the U.S. Embassy in Tunis, burning cars, storming the complex and replacing the U.S. flag with their own black banner, according to eyewitness accounts.
Aware that protests were planned for Friday -- the Muslim holy day -- the United States beefed up security at its embassies and consulates across the Middle East.
"We are in a full-court press at every single one of the posts in the Middle East and anywhere else there is any chance of demonstrations after Friday services to make sure nothing bad happens -- and to have the security in place in case bad things do happen," said a senior administration official, who was not authorized to discuss the issue in public and spoke on condition of anonymity.
The current unrest began Tuesday when outrage over a 14-minute American-made online video that mocks the Prophet Mohammed as a womanizer, child molester and ruthless killer sparked riots at the U.S. Consulate in Benghazi, Libya. Four America consulate staffers were killed, including U.S. Ambassador Chris Stevens.
U.S. officials suspect that a group sympathetic to al Qaeda used the protests over the film as cover for the complex and well-coordinated attack on the consulate.
Since then, there has been more outrage and violent protests over the online film, which YouTube has restricted in certain countries.
Here's a breakdown of where things stand:
People have taken to the streets in at least a dozen nations and territories to show their outrage about the film.
-- In Khartoum, Sudan, thousands of protesters converged on the German Embassy and set it on fire, a journalist on the scene said. Some managed to get inside and pull down a German flag before police with tear gas forced the crowd to retreat.
-- In Egypt, a running battle between police and protesters in Cairo continued into its fourth day. Egypt's influential and well-organized Muslim Brotherhood canceled nationwide protests planned for Friday, it announced on Twitter, but said a demonstration planned for Cairo's Tahrir Square would go ahead. At least 15 people were injured in demonstrations in Egypt on Friday, Health Ministry spokesman Mohamed Sultan said.
-- In Sudan's capital, Khartoum, thousands of protesters managed to get inside the Germany Embassy and pull down a German flag before police with tear gas forced the crowds to retreat. The German mission is next to the British Embassy, which is also facing protests, staff there said.
-- Afghanistan saw its first demonstrations Friday, despite the government's attempts to block the online video from sparking riots. Hundreds of demonstrators in the eastern Nangarhar province burned a U.S. flag and chanted "Death to America" and "We condemn the film." The demonstration lasted about an hour and ended peacefully, a local official said. The Afghan government has ordered an indefinite block of YouTube to prevent people there from watching the clips and staging violent protests.
-- In Gaza, several thousands people gathered after Friday prayers and chanted anti-American and anti-Israeli slogans. Protesters burned American and Israeli flags, as well as effigies of President Barack Obama.
-- In Syria, hundreds of protesters outside the U.S. Embassy in Damascus waved placards that condemned the film and blamed the U.S. administration for allowing the production and broadcast of it, according to the state-run Syrian Arab News Agency.
There were also protests in the Iranian capital, Tehran, as well as Baghdad, London, Jerusalem, and the southern Indian city of Chennai. Peaceful protesters congregated in Pakistan and Turkey to express their opposition to the online film.
The FBI and the U.S. Department of Homeland Security warned there could be more violence "at home and abroad as the film continues to gain attention."
The film that sparked the protests generated little interest when it was first posted in July on YouTube, but it received global attention after it was aired recently on Egyptian television and promoted by anti-Islam activists online.
U.S. authorities have discounted as false a producer's claims to news outlets that the filmmaker was an Israeli who made the movie with financing from more than 100 Jewish donors. Israel's government denies that the film's maker is Israeli.
Latest on the investigation into ambassador's killing
Sources tracking militant Islamist groups in eastern Libya say the attack that killed Stevens and three other Americans was most likely carried out by a pro-al Qaeda group. President Barack Obama has vowed that "justice will be done."
Four people have been arrested in connection with the attack, although they were not directly tied to the killings, said Monem Elyasser, the chief aide to the Libyan prime minister.
Elyasser did not release the identities nor did he detail the allegations against the four people in custody.
The evidence leading to the arrests was based partly on witnesses, but "mostly pictures that were taken around the compound at that time," Libyan Prime Minister Mustafa Abushagur told CNNI's Christiane Amanpour.
The first of two U.S. warships carrying guided missiles has arrived off the coast of Libya, and unmanned drones have been sent to help search for the killers.
A group of Marines called a Fleet Antiterrorism Security Team was deployed to Libya to help secure U.S. facilities, said two U.S. officials, who spoke on condition of anonymity because they were not authorized to release the information.
About 50 Marines arrived in the country Wednesday, the officials said.
CNN's Harmeet Singh, Kareem Khadder, Mohammed Tawfeeq, Arwa Damon, Ben Wedeman, Hamdi Alkhshali, Brian Walker and Elise Labott, and journalists Masoud Popalzai and Isma'il Kamal Kushkush contributed to this report.