U.S. envoys in the Middle East and North Africa are bracing for more protests and violence as outrage over an anti-Islam video continued to spread following a deadly attack on the American embassy in Libya.

After demonstrators attacked the U.S. embassy in Benghazi, where ambassador Chris Stevens and three other Americans were killed, other protests were reported in Yemen, Iraq, Iran and Morocco.

They are expected to intensify on Friday, after Egypt’s ruling Muslim Brotherhood, as well as officials in Iran and the Gaza strip, called on protesters to congregate in major cities after Friday prayers.

As a result, the U.S. put all of its overseas diplomatic missions on high alert, and even Canada closed its embassy in Cairo Thursday because of its proximity to the American embassy.

"It is important to note that as these protests are taking place in different countries around the world, responding to the movie, that Friday, tomorrow, has historically been a day when there are protests in the Muslim world," White House press secretary Jay Carney told reporters in Colorado. "And we are watching very closely for developments that could lead to more protests. We anticipate that they may continue."

Meanwhile, U.S. Secretary of State Hillary Clinton issued a stern condemnation of the video believed to have sparked outrage throughout the Muslim world, while saying it does not justify the violence or warrant a crackdown on free speech.

Clinton called the provocative video, which mocks Prophet Muhammad, "disgusting and reprehensible" on Thursday.

"It appears to have a deeply cynical purpose, to denigrate a great religion and to provoke rage," she said in Washington, D.C.

"The United States government had absolutely nothing to do with this video. We absolutely reject its content and message."

Despite its apparent intention to offend Muslims, Clinton said the video was not a justification for attacks on American officials, nor would it compel the U.S. government to curtail its citizens freedom of expression.

"Our country does have a long tradition of free expression, which is enshrined in our constitution and in our law," she said.

"We do not stop individual citizens from expressing their views no matter how distasteful they may be.

Outrage spreads

Clinton's remarks follow an apology from the Yemeni president, for a protest at the U.S. embassy in his country's capital Thursday.

Yemeni President Abed Rabbo Mansour Hadi issued his "sincere apologies" after hundreds of protesters stormed the U.S. embassy in Sanaa, entering the grounds where they burned the U.S. flag and hoisted a banner declaring "There is no God but Allah" in its place.

The demonstrators breached the perimeter, but did not enter the main building before they were dispersed by Yemeni security forces using tear gas and firing shots in the air.

Hadi called the mob a "rowdy crowd" intent on derailing his country's international relations with Washington.

Embassy spokesperson Lou Fintor has since told The Associated Press that no one was injured in the fracas and "all embassy personnel are safe and accounted for."

The attack was similar to the mob assaults that continued for a third day at the U.S. Embassy in Cairo, Egypt. Protesters there did not reach the embassy compound Thursday, but clashed with police in the area.

Egypt's Interior Ministry said at least 16 protesters and 13 police were wounded in the clashes, with 12 protesters arrested.

In Brussels for a visit to the European Union Thursday, Egyptian President Mohammed Morsi said his countrymen reject such "unlawful acts" and had communicated his condemnation of the attacks "in the clearest terms" during an overnight conversation with U.S. President Barack Obama.

Morsi also aimed some pointed criticism at the filmmakers behind the film believed to have set off the wave of anti-American rage.

"We condemn strongly ... all those who launch such provocations and who stand behind that hatred," Morsi said, adding that he had asked Obama "to put an end to such behavior."

Shiite followers of the anti-American cleric Muqtada al-Sadr took a similar message to the streets of the Iraqi capital Thursday, demanding the U.S. shut its embassy in Baghdad.

The Associated Press reports that protesters marched in the northeast Baghdad Shiite stronghold of Sadr City, burning U.S. flags and carrying banners declaring "We reject the attack on the Prophet Muhammad."

There are also reports that protesters gathered outside the Swiss Embassy in the Iranian capital. According to Iran's semi-official news agency, Fars, student protesters were directing their anger there, because the Swiss mission acts as a diplomatic proxy for the U.S. in Tehran.

Police had cordoned the area to keep protesters from entering the compound, Fars said.

There was reaction in Afghanistan too, where President Hamid Karzai cancelled a planned trip to Norway in favour of speaking with U.S. President Barack Obama by phone.

According to a statement issued by the Afghan government, Karzai conveyed his condolences and discussed the "film and the insulting of holy Islamic values," during their conversation.

The protesters' anger is believed to be linked to the movie "Innocence of Muslims," an Arabic-language version of which was posted on YouTube and had been broadcast on Egyptian television. Access to the inflammatory video clip was blocked in Egypt Wednesday.

In the English-language excerpts still accessible on the streaming video website, Islam's Prophet Muhammad is depicted as a womanizer and zealot calling for massacres.

American ambassador to Libya Chris Stevens and three other U.S. State Department officers were killed during an armed assault on the U.S. consulate in Benghazi, Libya on Tuesday.

U.S. officials were trying to determine whether the Benghazi attack was a planned act, rather than a spontaneous escalation of the protest, but there was no evidence to support that theory as of Thursday. There is also no evidence the attack was related to the 11th anniversary of the 9-11 attacks on the U.S., officials told AP.

In the wake of the deadly attack in Benghazi, the Pentagon has ordered two warships to take up positions off the coast of Libya.

The renewed violence and anti-American sentiment in the Middle East is not surprising since the region is so volatile, former Canadian ambassador to Egypt, Ferry de Kerckhove, told CTV’s Power Play Thursday.

Even after the Arab Spring uprisings that ousted Egypt’s dictator, Hosni Mubarak, it “doesn’t take much to push the buttons,” he said.