Security forces fired teargas to disperse stone-throwing demonstrators near the U.S. embassy in Cairo late on Wednesday, some 24 hours after protesters scaled the walls and tore down the flag over a film insulting the Prophet Mohammad.
State news agency MENA said some of those present had been injured, but gave no further details.
Live television showed hundreds of demonstrators gathered at the embassy, where late on Tuesday around 2,000 protested outside after some illegally entered the compound, ripped down the flag and burned it.
Washington has a big mission in Egypt, partly because of a huge aid programme that followed Egypt's signing of a peace treaty with Israel in 1979. The United States gives $1.3 billion to Egypt's military each year and offers the nation other aid.
Clashes between security forces and protesters continued in side streets near the building into the early hours of Thursday. Reuters witnesses saw protesters carrying petrol bombs and saw smoke billowing from one of the streets leading to the embassy.
MENA said earlier Egypt had arrested four people after Tuesday's demonstration in which protesters blamed the film on the United States.
It said the four people were transferred to the prosecutor's office, adding that security forces were still searching for others who scaled the walls of the U.S. mission.
<i>Writing by Edmund Blair and Shaimaa Fayed; Editing by Alison Williams</i>