Protesters shout outside the U.S. Embassy in Tunis, Tunisia, on Wednesday, September 12. Muslims throughout the Middle East held demonstrations outside U.S. missions to protest a movie deemed offensive to their religion and the prophet Mohammed. The U.S. ambassador to Libya, Chris Stevens, and three others were killed during a protest outside the U.S. Consulate in Benghazi, Libya. 
A group of protesters attend a demonstration outside the U.S. Embassy in Tunis on Wednesday. 
A demonstrator walks on a U.S. flag during a Wednesday's demonstration at the U.S. Embassy in Tunis. 
People inspect the damage at the U.S. Consulate in Benghazi, Libya, on Wednesday, the day after four people were killed. 
Egyptian demonstrators continue to stake out the U.S. Embassy in Cairo on Wednesday. 
Police confront protesters praying in front of the U.S. Embassy in Casablanca, Morocco, during a rally against the anti-Islam film on Wednesday. 
Moroccan women gather near the U.S. Embassy in Casablanca on Wednesday. 
A Palestinian man holds a placard praising Islam's prophet Mohammed during a demonstration against the film on Wednesday in front of the United Nations headquarters in Gaza City. 
Palestinian men burn the American flag during Wednesday's demonstration in Gaza City. 
A man waves his rifle as buildings and cars are engulfed in flames inside the U.S. Consulate compound in Benghazi, Libya, late on Tuesday, September 11. 
The U.S. Consulate in Benghazi is set on fire during a protest. Armed gunmen attacked the compound on Tuesday evening, clashing with Libyan security forces before the latter withdrew as they came under heavy fire. 
Protesters destroy an American flag pulled down from the U.S. Embassy in Cairo, Egypt. 
People stand around a drawing that says "Remember your black day 11 September" during the protest in Cairo. 
People shout and light flares in front of the U.S. Embassy in Cairo. 
People shout in front of the U.S. Embassy in Cairo. 
Protesters pull down a U.S. flag. 
Thousands angered by the film produced by expatriate members of Egypt's Christian minority in the United States protest outside the U.S. Embassy. 
Demonstrators yell outside the U.S. Embassy. 
Egyptian riot police stand guard as protesters climb down from the wall. 
An Egyptian protester waves a black flag inscribed with the Muslim profession of faith -- "There is no God but God, and Mohammed is the prophet of God" -- as he stands above the door of the U.S. Embassy. 
Protesters gather along the U.S. Embassy wall. 
- NEW: Riot police fire tear gas to repel rock-throwing protesters
- Egypt's president issues statement condemning film that incited rioters
- He did not condemn Tuesday's attack on the U.S. Embassy
- Rioters stormed the embassy and tore down the U.S. flag
Cairo (CNN) -- Riot police fired tear gas and warning shots late Wednesday outside the U.S. Embassy in Cairo as protesters tried for a second day to breach the building's perimeter, officials and witnesses said.
The clashes broke out amid heightened tensions at U.S. diplomatic missions in the region following a Tuesday night attack on the U.S. consulate in Benghazi, Libya, that left Ambassador to Libya Chris Stevens and three other consular officials dead.
Protesters gathered in Cairo, as they had a day earlier, to demonstrate against a film mocking Islam's prophet.
Wedneday night's protest turned violent as demonstrators began to throw rocks and push through barbed wire fencing outside the embassy, according to Alla Mahmoud, a spokesman for the Interior Ministry. One car was set on fire.
"Forces were able to push them down toward Tahrir Square farther from embassy street," Mahmoud said, adding that some arrests had been made.
More than a dozen people were injured in the clashes, which stretched past midnight, said Khaled Khatib of the health ministry.
Earlier, Egypt's president spoke in the "strongest terms" about the previous day's incident at the embassy -- but not against the attack.
WhiIe Egypt's prime minister called Tuesday's incident "regrettable" and unjustified, President Mohamed Morsy condemned the anti-Muslim film that incited the protesters.
Morsy made a reference to Egypt's duty to protect diplomatic missions and its opposition to unlawful protesters, but did not mention or criticize those who stormed the embassy.
"The presidency condemns in the strongest terms the attempt of a group to insult the place of the Messenger, the Prophet Mohammed (PBUH) and condemns the people who have produced this radical work," the president said in a statement posted on his Facebook page. "The Egyptian people, both Muslims and Christians, refuse such insults on sanctities."
The statement noted that "the Egyptian government is responsible to protect private and public properties and diplomatic missions in addition to embassy headquarters of various countries" and that "it respects and protects the right of expression and the right to protest peacefully under the law and will firmly oppose any irresponsible attempt to veer off the law."
Fringe group behind Libya attacks? 
Protesters storm US embassy buildings Protesters shout outside the U.S. Embassy in Tunis, Tunisia, on Wednesday, September 12. Muslims throughout the Middle East held demonstrations outside U.S. missions to protest a movie deemed offensive to their religion and the prophet Mohammed. The U.S. ambassador to Libya, Chris Stevens, and three others were killed during a protest outside the U.S. Consulate in Benghazi, Libya. A group of protesters attend a demonstration outside the U.S. Embassy in Tunis on Wednesday. A demonstrator walks on a U.S. flag during a Wednesday's demonstration at the U.S. Embassy in Tunis. People inspect the damage at the U.S. Consulate in Benghazi, Libya, on Wednesday, the day after four people were killed. Egyptian demonstrators continue to stake out the U.S. Embassy in Cairo on Wednesday. Police confront protesters praying in front of the U.S. Embassy in Casablanca, Morocco, during a rally against the anti-Islam film on Wednesday. Moroccan women gather near the U.S. Embassy in Casablanca on Wednesday. A Palestinian man holds a placard praising Islam's prophet Mohammed during a demonstration against the film on Wednesday in front of the United Nations headquarters in Gaza City. Palestinian men burn the American flag during Wednesday's demonstration in Gaza City. A man waves his rifle as buildings and cars are engulfed in flames inside the U.S. Consulate compound in Benghazi, Libya, late on Tuesday, September 11. The U.S. Consulate in Benghazi is set on fire during a protest. Armed gunmen attacked the compound on Tuesday evening, clashing with Libyan security forces before the latter withdrew as they came under heavy fire. Protesters destroy an American flag pulled down from the U.S. Embassy in Cairo, Egypt. People stand around a drawing that says "Remember your black day 11 September" during the protest in Cairo. People shout and light flares in front of the U.S. Embassy in Cairo. People shout in front of the U.S. Embassy in Cairo. Protesters pull down a U.S. flag. Thousands angered by the film produced by expatriate members of Egypt's Christian minority in the United States protest outside the U.S. Embassy. Demonstrators yell outside the U.S. Embassy. Egyptian riot police stand guard as protesters climb down from the wall. An Egyptian protester waves a black flag inscribed with the Muslim profession of faith -- "There is no God but God, and Mohammed is the prophet of God" -- as he stands above the door of the U.S. Embassy. Protesters gather along the U.S. Embassy wall. Protesters storm U.S. Embassy walls 
Middle East attacks against U.S. Several men scaled the walls of the U.S. Embassy in Cairo and tore down its American flag on Tuesday, the 11th anniversary of the 9/11 terrorist attacks. Police and army personnel formed defensive lines around the embassy in an effort to prevent demonstrators from advancing, but not before the protesters affixed a black flag atop a ladder in the American compound.
The flag that protesters hung in full view from inside the embassy complex was adorned with white characters that read, "There is no God but Allah and Mohammed is his messenger," an emblem often used by Islamic radicals.
A volley of warning shots were fired as a large crowd gathered around the compound, although it is not clear who fired the shots. There were no reported injuries or deaths.
Four protesters have been arrested in connection with the breach and were being questioned for "going off track to what is accepted as peaceful protesting," said Interior Ministry spokesman Alla Mahmoud.
The Cairo incident was not nearly as bad as the violence in neighboring Libya, where an attack on the U.S. Consulate in Benghazi killed four Americans, including Stevens. The Libya attack has been blamed on a pro-al Qaeda group, according to sources tracking militant groups in the region.
It's still unclear if the two attacks were coordinated. Protesters in both countries were upset over an online film that depicted Islam as a fraudulent religion and the Prophet Mohammed as a womanizer, child molester and ruthless killer.
In his statement, Morsy called on Egyptian diplomats in Washington "to take legal action against those people who seek to ruin relationships and discussions between people and countries."
The incident comes amid a delicate period in the diplomatic relationship between the United States and Egypt under Morsy, the country's first leader since the overthrow of longtime ruler Hosni Mubarak, a key Western ally.
Analysis: Morsy making up foreign policy as he goes along
Embassy officials issued a warning to Americans in Egypt, telling them to avoid the demonstrations which "may gather in front of the U.S. Embassy, or Egyptian government buildings such as the People's Assembly and Ministry of Interior."
Frenzied protesters could be seen Tuesday afternoon holding up bits of a shredded American flag to television camera crews while chanting anti-U.S. slogans.
"This is an expression of a feeling that is thought to be an insult," said Nizih El Naggary, a spokesman for the Egyptian Foreign Ministry. "But events like this are extremely deplorable. And we have to work to get things under control."
Egypt's foreign ministry pledged to protect embassies and warned of the protests' potentially debilitating effects on the Egyptian economy.
Several individuals claimed responsibility for organizing the demonstrations, including Salafist leader Wesam Abdel-Wareth, president of Egypt's conservative Hekma television channel.
Demonstrations elicited a mixture of reactions from the Egyptian street, where last year tens of thousands turned out in opposition to Mubarak.
"These protests are a bad image for Egypt," said a Cairo street vendor named Ahmed. "Of course I'm against insulting Islam, but it's the undereducated, poor people who are out here causing problems."
"All I want for Egypt is security and stability," he said. "And as you can see this isn't it."
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CNN's Mohamed Fadel Fahmy and Ian Lee in Cairo, Jomana Karadsheh, Matt Smith, Brian Walker, Elise Labott, Paul Cruickshank and Tracy Doueiry contributed to this report
