In the most recent attack on U.S. diplomatic posts in the Middle East, Muslim protesters stormed the U.S. Embassy compound in Yemen's capital, burning the American flag and smashing windows, Fox News reports. Protesters did not enter the main building housing the offices, but brought down the U.S. flag in the courtyard, burning it and replacing it with a black banner reading "There is no God but Allah." Yemeni security forces used tear gas to disperse the demonstrators, driving them out of the compound after about 45 minutes. It was unclear whether anyone was inside the embassy at the time of the attack. Officials said the Pentagon was monitoring the situation in Yemen, but so far had received no request for military assistance there. Meanwhile, protests continued outside the U.S. Embassy in Cairo, Egypt for the third day in a row; warning shots and tear gas were fired on demonstrators who clashed with police near the embassy. The violence has raised worries that further protests could break out around the Muslim world as anger spreads allegedly over a film ridiculing Islam's prophet Mohammed -- but the U.S. is investigating whether Tuesday's deadly assault on the consulate in Libya was a planned terrorist strike to mark the anniversary of 9/11.