Chanting "death to America," hundreds of protesters angered by an anti-Islam film stormed the U.S. Embassy compound in Yemen's capital and burned the American flag on Thursday, the latest in a series of attacks on American diplomatic missions in the Middle East. American missions have been attacked this week in three Arab nations — Yemen, Egypt and Libya — that have faced persistent unrest and are struggling to restore law and order after last year's revolts deposed their authoritarian regimes. The protests in Yemen and Egypt point to an increased boldness among Islamists who have become more powerful amid the turmoil since the revolts. In the past, protests have broken out over perceived insults to Islam from the West, but in Arab countries they never escalated to the degree of breaching embassies, suggesting now Islamists feel they can act with impunity. The violence this week in Libya was of a different degree altogether. While protesters in other countries were unarmed, a crowd bristling with machine guns and rocket-propelled grenades overwhelmed the American Consulate in Benghazi late Tuesday, killing the ambassador and three other Americans and ransacking the building. U.S. officials suspect the assault may have been a planned operation rather than a spontaneous mob assault. In the Yemeni capital on Thursday, protesters smashed windows as they breached the embassy perimeter and reached the compound grounds, although they did not enter the main building housing the offices. Angry young men brought down the U.S. flag in the courtyard, burned it and replaced it with a black banner bearing Islam's declaration of faith — "There is no God but Allah." Yemeni security forces who rushed to the scene fired in the air and used tear gas to disperse the demonstrators, driving them out of the compound after about 45 minutes and sealing off the surrounding streets. It was not immediately clear whether anyone was inside the embassy at the time of the attack. Demonstrators removed the embassy's sign on the outer wall, set tires ablaze and pelted the compound with rocks. The Yemeni Embassy in Washington condemned the attack and vowed to ensure the safety of foreign diplomats and to step up security measures around their missions in the country. It was similar to an attack on the U.S. Embassy in the Egyptian capital on Tuesday night. A mob of Libyans also attacked the U.S. consulate in the eastern city of Benghazi on Tuesday, killing American Ambassador Chris Stevens and three other Americans.