"Today's presidential election in Syria is a disgrace. Assad has no more credibility today than he did yesterday," State Department spokeswoman Marie Harf said.
Voters turned out in government-controlled areas of Syria to vote in an election seen as certain to return long-standing leader Assad to office with a mandate to continue his battle against rebel forces.
At least 162,000 people have been killed in Syria since an uprising against Assad's rule erupted in March 2011, triggering a savage crackdown. More than half the population have fled their homes.
Harf said the decision to hold elections was "detached from reality" and part of "a 40-year legacy of violent repression.