Cairo - Fury over an anti-Islam film spread across the Muslim world Friday, with deadly clashes near Western embassies in Tunisia and Sudan, an American fast-food restaurant set ablaze in Lebanon, and international peacekeepers attacked in the Sinai despite an appeal for calm from Egypt's Islamist president.

At least four people - all protesters - were killed and dozens were wounded in the demonstrations in more than 20 countries from the Middle East to Southeast Asia. Most were peaceful but they turned violent in several nations, presenting challenges for the leaders who came to power in the Arab Spring.

Security forces worked to rein in the anti-American crowds but appeared to struggle in doing so. Police in Cairo prevented stone-throwing protesters from getting near the U.S. Embassy, firing tear gas and deploying armored vehicles in a fourth day of clashes in the Egyptian capital. One person died there after being shot by rubber bullets.

The State Department said U.S. Embassy personnel were reported to be safe in Tunisia, Sudan and Yemen - sites of Friday's violent demonstrations.

President Barack Obama said Washington would "stand fast" against attacks on U.S. embassies around the world. He spoke at a somber ceremony paying tribute to four Americans - including U.S. Ambassador Chris Stevens - killed earlier this week when the U.S. Consulate in Benghazi, Libya, was stormed by militants who may have used protests of the anti-Muslim film as cover to stage an assault on the 11th anniversary of the Sept. 11 terrorist attacks.

Secretary of State Hillary Rodham Clinton had tried to pre-empt the violence a day earlier by saying the rage and violence aimed at American diplomatic missions was prompted by "an awful Internet video that we had nothing to do with."

But the demonstrators came out after weekly Friday prayers. Many clerics in their mosque sermons urged congregations to defend their faith, denouncing the obscure movie "Innocence of Muslims" that was produced in the United States that denigrated the Prophet Muhammad.

In addition to countries where protests have occurred, U.S. embassies around the world, including in France and Austria, issued alerts Friday advising Americans to review their personal security measures and warning them that demonstrations may occur and may turn violent.

The heaviest violence came in Khartoum, Sudan, where a prominent sheik on state radio urged protesters to march on the German Embassy to protest alleged anti-Muslim graffiti on mosques in Berlin and to the U.S. Embassy to protest the film.

On Friday night, a U.S. official said a Marine rapid response team was headed to Sudan. The official spoke on condition of anonymity since the deployment had not been made public.

Soon after, several hundred Sudanese stormed into the German Embassy. Protesters celebrated until police firing tear gas drove them out. Some then began to demonstrate outside the British Embassy.

Several thousand then moved via a convoy of buses to the U.S. Embassy on Khartoum's outskirts where they clashed with Sudanese police who dispersed the crowd with tear gas, starting a stampede. Witnesses reported seeing three protesters motionless on the ground, although there was no word whether they were dead or alive.

Additional reporting by Mohamed Osman in Khartoum, Sudan.