“The U.S. should apologize to the whole Islamic community. And those Copts should be put to trial and they should be hanged,” said Mohammed Ahmed, 28, a chef, referring to two Coptic Christians in the United States who’ve been linked to the video. Plumes of tear gas hovered overhead as he spoke and, nearby, other young men were setting fires. The streets were littered with rocks and other debris thrown at and by security forces.

Nearby, Mustafa Amin, 26, an unemployed teaching school graduate, proposed an international law “that would criminalize any assault on the prophet. And it should be under the supervision of the United Nations.”

Egypt was not alone in stepping up security outside U.S. diplomatic facilities. In Yemen’s capital, Sanaa, police armed with water cannons made heavy use of tear gas and warning shots to keep protesters from reaching the U.S. Embassy, where on Thursday angry demonstrators had stormed the heavily guarded compound.

Diplomatic outposts were not the only American symbols targeted on Friday. In Tripoli, Lebanon, protesters set fire to a building containing Hardees and KFC restaurants. One person died in the blaze.

There were also peaceful demonstrations. In Indonesia, the world’s most populous Muslim nation, thousands of protesters gathered in front of the U.S. Embassy in Jakarta without violence.

Meanwhile, Obama administration officials worked hard to dispel a series of rumors that flew around the Internet, from allegations that Marines at embassies around the world had been ordered not to carry live ammunition to allegations that the embassy in Cairo had been warned about the likelihood of violence but had failed to take precautions.

A U.S. intelligence official acknowledged that a cable had been sent to the embassy in Cairo advising diplomats that the video, which had been on the Internet since July, had been receiving increasing attention. But the official, who asked not to be identified because he was not authorized to discuss the matter, said the cable was not a warning of upcoming violence.

“It was a very routine type of cable drawing attention to the video,” the official said. “We look at these things and we can see when something is getting attention. You begin to see it start to get attention, there is chatter, people looking at it. We basically said that it’s getting more attention and we want you to be aware."

Nuland, briefing reporters in Washington, said that since Tuesday, 65 American embassies have issued 88 security warnings to Americans living in their areas reminding them of the tense climate.

Matthew Schofield in Washington and special correspondents Adam Baron in Sanaa, Yemen, and Alan Boswell in Nairobi, Kenya, contributed.