The National Air and Space Museum in Washington was closed after more than 100 anti-war protesters tried to push their way into the building on Saturday afternoon.
Security guards at the Smithsonian museum used pepper spray and one person was arrested.
Demonstrations began in the capital on Thursday on the 10th anniversary of the start of the Afghanistan war.
Meanwhile, the Occupy Wall Street movement, which is protesting against banks, unemployment and corporate greed in the United States, is spreading outside New York.
Protests are happening in other cities including Chicago, Seattle, Los Angeles, Philadelphia, Houston and Tennessee.