The US government has branded Venezuela’s President Nicolás Maduro “a dictator” and frozen any US assets, after he held a controversial poll to elect a constituent assembly.
Under the sanctions, US firms and individuals are banned from doing business with Mr Maduro.
The election on Sunday was marred by violence, with widespread protests and at least 10 people killed.
President Maduro hailed the poll as a “vote for the revolution”.
The opposition coalition, which boycotted the election, said 88% of voters had abstained. It has refused to recognise the election. Electoral officials said the turnout was 41.5%.
Protesters have blocked a number of roads in the capital, Caracas, and will hold a march later on Monday to honour those killed on polling day.
Venezuela’s attorney general, Luisa Ortega, a vocal critic of the Maduro government, called the vote an expression of “dictatorial ambition”.
The US had previously warned that it would not recognise the election, with President Donald Trump vowing “strong and swift economic actions” if it went ahead.
The sanctions were announced in a statement by US Treasury Secretary Steven Mnuchin.
“Yesterday’s illegitimate elections confirm that Maduro is a dictator who disregards the will of the Venezuelan people,” he said.
“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.”
US National Security Adviser HR McMaster also condemned the “outrageous seizure of absolute power”, calling the vote “a very serious blow to democracy in our hemisphere”.
On 26 July, the US Treasury had imposed sanctions on 13 current and former Venezuelan officials in a bid to deter Mr Maduro from holding the poll.
Those targeted include the interior minister and the head of the army.
“Who do these imperialists in the United States think they are?” Mr Maduro said in response to these sanctions. “The government of the world?”
He called the sanctions “illegal, insolent and unprecedented”.
Since the results of the vote emerged, the EU has also expressed “preoccupation for the fate of democracy in Venezuela”, and said it doubted it could accept the results.
However, Russia, Cuba, Nicaragua and Bolivia have stood by Mr Maduro.
Venezuela’s 30 million citizens are suffering through shortages of basic goods and medicines, as the country’s weakened economy declines still further.
A wave of anti-government protests has left more than 120 people dead in four months.