US missions are on high alert across the Muslim world as anger grows over a film made in American that mocks Islam.
In the Egyptian capital, Cairo, protesters on Friday hurled stones at a line of police blocking their way to the US embassy, which was attacked earlier this week.
Police in riot gear fired tear gas and threw stones back at the demonstrators. A burnt-out car was overturned in the middle of the street which leads to the fortified embassy from Tahrir Square.
Police had tried to clear the Tahrir Square on Friday ahead of a nationwide protest called by the Muslim Brotherhood, Egypt's most influential group, Reuters reports.
But shortly after the square was cleared the demonstrators returned, waving green and black flags with Koranic verses on them.
More anti-American demonstrations are expected after prayers on Friday.
In Yemen, hundreds of protesters broke through the main gate of the heavily fortified compound in the capital, Sanaa, on Thursday.
Reuters reports they smashed windows of security offices outside the embassy and burned cars before the Yemeni government ringed the area with troops.
A security source said at least 15 people were wounded, some by gunfire. An embassy spokesman said its personnel were safe.
On Wednesday, US ambassador to Libya Chris Stevens and three other officials were killed in a fire started after the American consulate in Benghazi was stormed.
Bangladeshi Islamists tried to march on the US embassy in Dhaka and Iranian students protested in Tehran.
Earlier in the week, there were protests outside US missions in Tunisia, Sudan and Morocco directed at the American-made film Innocence of Muslims.
President Barack Obama has vowed to bring to justice the Islamist gunmen responsible for the deadly attack on the US American consulate in Libya.
Libyan prime minister Mustafa Abu Shaqur says four arrests have been made in connection with the attack.