National Security Council head H. R. McMaster told reporters: "Maduro is not just a bad leader. He is now a dictator."
The new sanctions will freeze any of Maduro's assets under U.S. jurisdiction, though the White House didn't comment on what those assets might be. The measures also block U.S. persons from dealing with Maduro.
Maduro recently declared victory in a nationwide vote to form a new governing body that can rewrite Venezuela's constitution. The opposition boycotted the vote, arguing it would give Maduro undemocratic new powers.
The country was gripped by widespread, and sometimes violent, protests during the months leading up to the vote. Around 120 people have been killed in the past four months of unrest.