The Trump administration imposed sanctions on Venezuelan President Nicolas Maduro on Monday following what it called a "sham" election of a new, powerful legislative assembly on Sunday.

The Treasury Department added Maduro to a list of sanctioned former and current Venezuelan government and military officials. The move freezes his assets in the U.S., bans travel and prohibits U.S. business transactions with the Venezuelan president.

"Yesterday's illegitimate elections confirm that Maduro is a dictator who disregards the will of the Venezuelan people," Treasury Secretary Steven Mnuchin said Monday. "By sanctioning Maduro, the United States makes clear our opposition to the policies of his regime and our support for the people of Venezuela who seek to return their country to a full and prosperous democracy."

Ahead of Sunday's election, Trump threatened "strong and swift economic actions" against Maduro's government if the contest took place.

U.S. Ambassador to the United Nations Nikki Haley criticized Sunday's election as a "sham" and said it is "another step toward dictatorship."

The U.S. government has threatened to sanction the 545 members of the new legislative body once they assume their positions in the next two days. That includes Cilia Flores, Maduro's wife, and Diosdado Cabello, a congressman.

The new constituent assembly will meet in the coming days to discuss rewriting Venezuela's constitution.

The Trump administration has so far stopped short of implementing a ban on Venezuelan oil imports, considered the most severe sanction. Instead, the administration is exploring sanctions similar to those imposed against Russia.

The Venezuelan government said 8 million people voted in Sunday's election, but that figure has been disputed by those who oppose Maduro.

Violence erupted on the streets during the election as government forces challenged protesters opposing Maduro. Sixteen people were reported dead.