The United States on Monday branded Venezuelan President Nicolas Maduro a "dictator" threatening his country's democracy and imposed sanctions targeting any assets he might hold on US territory.

"Yesterday's illegitimate elections confirm that Maduro is a dictator who disregards the will of the Venezuelan people," US Treasury Secretary Steven Mnuchin said in a statement announcing the action.

Sunday's vote in Venezuela to elect a Constituent Assembly that would supersede the country's opposition-controlled National Assembly has earned international scorn, with the US leading a group of nations refusing to recognize the election.