The New York City gathering included anti-war activists, anti-Wall Street activists, and also some Syrian expatriates who said they supported the regime of Bashar Assad. Some carried signs saying, "No more wars for corporate profit," and "Cut the Pentagon, not food stamps."
In Washington, dozens of protesters chanted and picketed, saying Congress shouldn't authorize military action.
President Barack Obama has called on Congress to approve the use of military force in the wake of a deadly chemical weapons attack his administration blames on the Syrian government. The first votes on the measure could come Wednesday.