CAIRO (CNN) -- Protests over an offensive anti-Muslim film bled into a third day Thursday near the U.S. Embassy in Cairo.
Demonstrators threw rocks and Molotov cocktails as police tried to disperse them by firing tear gas canisters from police vehicles as they drove through Tahrir Square, near the embassy.
At least 13 protesters and six police officers were injured, Egyptian government officials said Thursday.
The clashes came amid heightened tensions at U.S. diplomatic missions in the region following Tuesday's attack on the U.S. Consulate in Benghazi, Libya, that left Ambassador Chris Stevens and three other consular officials dead.
That same day, the 11th anniversary of the 9/11 terrorist attacks, several men scaled the walls of the U.S. Embassy in Cairo and tore down its U.S. flag.
The protests follow the online release of a film produced in the United States that denigrates Prophet Mohammed.
About 500 people, many chanting anti-American slogans, demonstrated Wednesday in Cairo against the film. The protest continued into Thursday.
The protest turned violent as demonstrators threw rocks and pushed through barbed wire fencing outside the embassy, according to Alla Mahmoud, a spokesman for the Egyptian Interior Ministry. Two police trucks and a car were set afire.
"Forces were able to push them down toward Tahrir Square farther from embassy street," Mahmoud said, adding that some arrests had been made.
By early Thursday, protesters had been pushed 100 yards from the embassy, said journalist Ian Lee in Cairo.
Earlier, Egypt's president spoke in the "strongest terms" about Tuesday's incident at the Cairo embassy -- but not against the attack.
Tuesday, police and Egyptian army personnel formed defensive lines around the U.S. Embassy to prevent demonstrators from advancing, but not before the protesters placed a black flag atop a ladder in the American compound. Police arrested four protesters.
WhiIe Egypt's prime minister called Tuesday's incident "regrettable" and unjustified, its president condemned the anti-Muslim film that incited the protesters.
President Mohamed Morsy made a reference to Egypt's duty to protect diplomatic missions and its opposition to unlawful protesters, but did not mention 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 ... 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."
The incident comes during a delicate period in the relationship between the United States and Egypt under Morsy, the country's first leader since the overthrow last year of longtime ruler Hosni Mubarak -- a key Western ally.
U.S. President Barack Obama spoke with Morsy on Wednesday "to review the strategic partnership between the United States and Egypt, and our ongoing efforts to strengthen bilateral economic and security cooperation," the White House said in a statement early Thursday.
During the call, the statement said, Obama told Morsy that "he rejects efforts to denigrate Islam, but underscored that there is never any justification for violence against innocents and acts that endanger American personnel and facilities."
Morsy "expressed his condolences for the tragic loss of American life in Libya and emphasized that Egypt would honor its obligation to ensure the safety of American personnel," according to the White House statement.
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. A pro-al Qaeda group was to blame for that attack, according to sources tracking militant groups in the region.
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."