Egyptian security forces have sealed off the area near the U.S. Embassy in Cairo, one of several cities across the Muslim world where protesters demonstrated against an anti-Islamic video posted on the Internet.

Egyptian forces took dozens of protesters into custody overnight following a fourth day of violent demonstrations in Cairo and other cities in various countries.

From Tunisia to Egypt, Sudan to Yemen, protesters laid siege to embassies of the U.S. and its allies, denouncing the video and those they feel have not done enough to stop it. At least two deaths have been reported.

Some of the most violent demonstrations took place Friday in the Sudanese capital where angry crowds clashed with police after descending on embassies belonging to the United States, Britain and Germany. Witnesses said at least one protester was killed outside the U.S. embassy.

Another person was killed in protests in northern Lebanon.

Protesters stormed the U.S. Embassy in Tunis and set fires.

At an air base outside Washington, U.S. President Barack Obama and Secretary of State Hillary Clinton watched, then paid tribute, as the bodies of four Americans killed in Libya earlier this week came home.

U.S. Ambassador to Libya Christopher Stevens and three of his staffers were killed at the U.S. consulate in Benghazi on Tuesday after protesters, upset over the film, attacked the building.

The ongoing violent protests have prompted a new round of calls for calm.

U.N. Secretary-General Ban Ki-moon Friday called the film sparking the protests “shameful” but warned protest leaders that exploiting the anger “only feeds the cycle of recrimination and senseless violence.”

U.S. and other foreign missions stepped up security following violent attacks that began Tuesday.

In Benghazi, Libya, where the U.S. ambassador and three other American personnel were killed, security was stepped up around the city and the airport temporarily closed. U.S. warships are headed to the Libyan coast, while additional U.S. Marine guards are deployed to protect the American embassy in Yemen that was breached by protesters Thursday.

In Tunisia, gray smoke rose above the U.S. embassy in Tunis Friday where protesters clashed with police and some managed to jump the wall surrounding the building. Police in the Nigerian city of Jos said they had to fire into the air to disperse hundreds of young protesters.

Angry protesters also clashed with international peacekeepers in Egypt's Sinai Peninsula, setting fire to their base, not far from the Gaza border. Protests also took place in Jerusalem, Gaza, India, Malaysia, Indonesia and Yemen.

In many Cairo mosques Friday, the video, a crudely-made attempt to mock the Prophet Muhammad, was the topic of the day. One imam reminded worshippers that Egyptians, under their new, Islamist government, can now openly defend the prophet from such insults.

Egyptian President Mohamed Morsi, who has condemned the video, spoke out again Friday on the need to keep protests in check.