Turmoil spreads across Muslim world over controversial Mohammed film Each demonstration involved only hundreds of people, but with anger mounting over what is being seen as the latest Western insult of Islam there were predictions that the worst is still to come. With Egypt's Muslim Brotherhood calling for a "million-man march" on the streets of Cairo after noon prayers on Friday, governments across the Islamic world braced themselves for a potentially much more violent outpouring of public anger. Barack Obama said he had ordered his administration to do whatever is necessary to protect Americans abroad. Speaking at a re-election campaign rally in Colorado, he and his aides had been in contact with other governments "to let them know they've got a responsibility to protect our citizens." Yemeni men break a window of the US embassy in Sana'a, during a protest against the American film "Innocence of Muslims" Hamid Karzai, the Afghan president, postponed a visit to Norway to deal with the threat, while Nigeria and the Philippines stepped up security outside foreign embassies. Hillary Clinton, the US secretary of state, attempted to quell the rage by distancing the United States from the film, a barnyard production of mysterious provenance that portrayed Mohammed as a histrionic paedophile and homosexual. "To us, to me personally, this video is disgusting and reprehensible," she said. It appears to have a deeply cynical purpose, to denigrate a great religion and to provoke rage. The United States government has absolutely nothing to do with this video. We absolutely reject its content and message. But with President Barack Obama's hopes of foresting more positive feelings towards the United States in the Arab world appearing to have failed, it was unclear whether Mrs Clinton's words would have much of an impact. The scenes at the US embassy in Sana'a, the Yemeni capital, suggested they would not. As clouds of black smoke filled the sky, hundreds of Yemenis stormed the mission, easily overwhelming local security forces guarding a rear entrance to the building's compound. Shouting "God is Great," they burnt an American flag, set fire to tires, destroyed at least five cars and attempted to loot embassy offices before they were dispersed by police who, according to witnesses, were initially overwhelmed by protesters. Unlike the assault on the US consulate in Benghazi, which came under a ferocious rocket-propelled grenade attack, the protesters in Sana'a were not armed. A vehicle burns during clashes outside the US embassy in Cairo, Egypt, as part of widespread anger across the Muslim world. But there were suspicions that at least part of the protest was orchestrated rather than spontaneous after a group of men wearing masks arrived to join a protest that had initially been peaceful. Although the protests across the region could accrue a momentum of their own, some diplomats have expressed concern that Islamist militants are seeking to manipulate demonstrations in the hope of sparking violence. Yemen, in particular, has seen Islamist militant groups attack Western diplomats in the past, with both the British ambassador and deputy ambassador surviving assassination attempts in 2010. The deputy head of al-Qaeda's Yemeni wing, Said al-Shehri, was allegedly killed in an army operation this week, raising fears that the group could seek to retaliate against American interests. The United States has carried out drone strikes against the group in recent years. For all their vitriol, the protesters represent a small minority. Many Arabs have expressed their opposition to the film but are far more outraged by the violence it has ostensibly triggered. "The film is an insult to the Prophet, but this is unbelievable," said a shopkeeper whose store was adjacent to the US embassy in Sana'a. We're really struggling to understand how something like this could get so out of hand. Hisham Matar, the celebrated British-Libyan novelist, said that the majority in Benghazi shared similar views. He reported a deep sense of shame in the city, where demonstrations - this time appearing genuinely spontaneous - erupted to denounce the killing of the American diplomats. Officials in Libya said an investigation had been opened into the attack and reported that "several" people had been arrested. The president of Yemen and Libyan leaders were quick to apologise to the United States, although criticism has been levelled at Egypt's Islamist president, Mohammed Morsi, for being slower off the mark. After a day of silence, Mr Morsi finally condemned the attack on the US embassy in Cairo. "We condemn strongly ... all those who launch such provocations and who stand behind that hatred," he said. But at the same time we say this cannot be taken as a justification for attacking embassies or consulates. The Egyptian state is responsible for protecting embassies and consulates, and the Egyptian people will not engage in these ... unlawful acts.