Angry protesters stormed the US embassy in Cairo on Tuesday, scaling one of the compound's walls to tear down American flags and replace them with black flags bearing what CNN called "Islamic emblems."

In response, embassy security guards fired "a volley of warning shots," according to a CNN producer who was at the scene. On a prior warning, the embassy had already been cleared of personnel before the protests began, CNN noted. An emergency message posted to the embassy's website had warned US citizens of "possible demonstrations" near the embassy on Sept. 11.

The Associated Press described most of the protestors, who were said to be angry because of a film that was produced in the United States that they believe denigrates the Prophet Muhammad, as "ultra conservative Islamists." The AP reported that the inscriptions on the flags protested the offending film.

The AP said that the film, which it didn't name, "show[s] the prophet having sex and question[s] his role as the messenger of God's words."

GlobalPost correspondent Erin Cunningham, who is in Cairo, said that the film is "Mohammed Nabi al-Muslimin," which translates to "Mohammed, Prophet of the Muslims." The film is said to have been produced by "infamous Quran-burning preacher" Terry Jones, in the words of Foreign Policy, "in collaboration with a group of Egyptian Copts."

The Atlantic posted video from YouTube that they said had been verified as a scene from the film by a Coptic specialist at the Hudson Institute.

GlobalPost's Cunningham wrote on Tuesday afternoon: "As far as I know, the black flags are still up, and the protests are still going — growing, in fact. They've also tagged the Islamic creed, or declaration of belief — 'There is only one God but God, and Muhammad is his messenger' — on the entrance of the embassy building."

She added that the protestors hail from a few specific groups:

"The protests are dominated by the reactionary fringe — the fundamentalist Muslims, or Salafis. But there are also non-extremists there as well, including football fans, known as "Ultras," and some from Egypt's Coptic Christian minority. "It seems odd that Copts, who have often expressed fear of the rising tide of Islamism in Egypt, would be joining the extremists to protest the United States. But earlier today, Egypt's Coptic Church released a statement condemning the film, stressing Muslim-Christian harmony in Egypt. "As for the Ultras, they're normally at the forefront of any Cairo protest — and are around to do the heavy lifting like scaling or tearing down walls, and hanging flags. That's not to say they're not there to protest the film, but they're known for bringing energy to Egypt's protest crowds."

Cunningham added that there was no official presence of the Muslim Brotherhood or their political arm at the protests.

Later in the day, the US embassy in Cairo posted a press release to its website condemning what it called "religious incitement."

"The Embassy of the United States in Cairo condemns the continuing efforts by misguided individuals to hurt the religious feelings of Muslims," the statement said.

Noting the significance of the protest's timing, the statement continued: "Today, the 11th anniversary of the September 11, 2001 terrorist attacks on the United States, Americans are honoring our patriots and those who serve our nation as the fitting response to the enemies of democracy. Respect for religious beliefs is a cornerstone of American democracy."

Erin Cunningham contributed reporting from Cairo.