Updated 6:08 p.m. ET
(CBS/AP) Worldwide Muslim anger over a film mocking Islam's prophet continued to spread Thursday, prompting President Barack Obama to issue a warning to countries where Americans may be in danger.
President Obama, speaking at a re-election campaign rally in Golden, Colorado, said his administration had been in contact with other governments "to let them know they've got a responsibility to protect our citizens."
The president also said on Thursday: "I've directed my administration to do whatever is necessary to protect all Americans serving abroad".
American diplomatic offices everywhere have seen their security beefed up, and there are contracted aircraft being kept on the runways in major cities so that they can ferry out evacuated personnel.
The spreading violence comes as outrage grows over an obscure movie made in the United States called "Innocence of Muslims" that mocked Islam's Prophet Muhammad.
The first of the protests against the film began in Cairo, Egypt, outside of the U.S. Embassy there, on Tuesday. Protesters rushed embassy grounds, taking down and tearing up the American flag flying at half-mast in commemoration of 9/11 before security forces turned them away.
The protests in Egypt continued Thursday, with protesters clashing with police near the U.S. mission. Egypt's Islamist President Mohammed Morsi condemned the attack on Libya that killed the American ambassador and vowed Thursday to protect foreign embassies in Cairo, where police were using tear gas to disperse protesters at the U.S. mission.
In Libya on Tuesday, four diplomatic personnel, including the ambassador to Libya, Chris Stevens, were killed in what appears to have been a coordinated attack that took advantage of a protest against the film in Benghazi, once the seat of the Libyan revolution. FBI agents are on the ground there investigating whether there were al Qaeda links to the attack, and American security forces have engaged in what appears to be a terrorist manhunt.
By Thursday, other Muslim countries had taken up protests against the film, including in Yemen, where anti-U.S. protesters and Yemeni police clashed at the U.S. Embassy in Sanaa. CBS News sources say a large group of protesters reached the walled compound, but failed to breach any of the buildings inside the compound as police fired warning shots to try to disperse the crowd.
The number of protesters in Sanaa was estimated between 3,000 and 4,000, according to sources speaking to CBS News partner network Sky News. As protests continued late into Thursday, and there were unconfirmed reports of protesters killed.
CBS News correspondent David Martin reports an elite Marine anti-terrorist team has landed in Yemen, similar to the one sent to Libya this week to protect and evacuate diplomatic personnel after the attack in Benghazi.
Yemen is the home of al Qaeda in the Arabian Peninsula (AQAP), one of the most active and dangerous terror groups linked to the central al Qaeda organization. The U.S. military and intelligence agencies have worked alongside Yemeni officials to counter the Islamic extremist element inside the country. Many drone strikes have been carried out, allegedly by the U.S., in the last year targeting militants in Yemen.
In Iraq, hundreds of followers of the anti-American Shiite cleric Muqtada al-Sadr demanded the closure of the U.S. Embassy in Baghdad - the largest American diplomatic mission in the world - because of the film. Thousands marched in the Shiite stronghold of Sadr City in northeast Baghdad and shouted, "No, no, to Israel! No, no to America!" and "Yes, yes for Messenger of God."
An Iran-backed Shiite militant group threatened U.S. interests in Iraq with its militia's leader, Qais al-Khazali, telling the AP that the amateurish movie was unforgiveable. He called on all Muslims to "face our joint enemy." An estimated 15,000 employees work at the U.S. embassy.
Large protests were expected in Baghdad and Iraq's second largest city, Basra, after Friday prayers.
Iranian students protested against the film outside the Swiss embassy in Tehran, according to FARS, the semi-official state news agency. The AP put the number of protesters at about 50. America doesn't have an official diplomatic presence in Iran, but the Swiss look after U.S. interests. The students burned an American flag and chanted "Death to the U.S." and "Death to Israel," according to FARS.
In Afghanistan, the government in Kabul has sought to avert protests, given that anger over perceived insults to Islam has triggered violence in the past. President Hamid Karzai canceled an official visit to Norway and spoke by phone with Obama to convey his condolences for the deaths of the U.S. ambassador to Libya and three other diplomats. He also discussed the "film and the insulting of holy Islamic values."
A Shiite cleric condemned the film during a sermon in a mosque west of Kabul. Sayyed Eisa Hossaini Mazari told about 200 worshippers in a mosque west of Kabul that a "dirty American made a movie and it was put on YouTube." Mazari did not directly call for demonstrations in Afghanistan, but told the AP there will be protests if there is no "U.S. action against the movie."
In Gaza, about 150 Muslim clerics and lawmakers from the ruling Hamas movement staged a protest outside the parliament building in Gaza City to condemn the film. They accused Israel and the West of stoking up sectarian tensions in the region and pitching Muslims against Christians.
Hamas and the smaller militant group Islamic Jihad are calling for large protests across Gaza on Friday.
In Jordan, calls by several Muslim opposition groups for protests at the U.S. Embassy in the capital Amman went ignored. A banned extremist Islamic movement with links to al Qaeda called on its followers to attend a demonstration outside the American embassy compound after Friday prayers.
Israeli police said they were stepping up security ahead of Friday prayers in Jerusalem. Police spokesman Micky Rosenfeld said that "tensions have been felt." He said a larger number of officers would be deployed around Jerusalem's Old City, where the Al-Aqsa mosque, Islam's third-holiest site, is located.
In Dhaka, Bangladesh, police stopped a march by about 400 people who burned a U.S. flag several miles from the U.S. Embassy, where higher security was evident.
Police in Nigeria, which faces an Islamist insurgent threat, ordered 24-hour security around all foreign embassies on Thursday, Reuters reports. The American embassy in Abuja issued an emergency warning to its citizens living in Nigeria, where radical Islamist sect Boko Haram has killed hundreds this year in an insurgency against the Nigerian government.
There have also been reports of anti-American protests this week in Tunisia, Sudan and Morocco.