The United States has sent Marines from the Fleet Anti-terrorism Security Team to help protect its embassy in Yemen during demonstrations, the Pentagon said Friday.

"A FAST platoon is now on the ground in Sanaa," spokesman George Little told reporters, describing the deployment of the 50-strong unit as a "precautionary step" amid anti-American unrest in the Middle East.

Little told reporters there were no immediate plans to evacuate the Yemen embassy, but that security would be stepped up.

Earlier, Yemeni security forces had fired warning shots and water cannon to disperse hundreds of protesters trying to reach the US embassy in Sanaa after Friday prayers.

The protesters, angered by a film produced privately in the United States and deemed insulting to Islam, gathered about 500 meters (yards) away from the embassy compound and burnt the American flag.

Similar protests were also underway outside Yemen in other cities with large Muslim populations, including Cairo, Khartom, Tunis, Lahore and Mumbai.