The US has imposed sanctions on Venezuela's state-owned oil firm PDVSA and urged the country's military to accept a peaceful transfer of power. National Security Adviser John Bolton said President Nicolás Maduro and his allies could no longer loot the assets of the Venezuelan people. Efforts by the opposition to unseat Mr Maduro have increased in recent days.
The US and more than 20 countries have recognized opposition leader Juan Guaidó as interim president.
Treasury Secretary Steven Mnuchin said the proceeds of the purchase of Venezuelan oil would now be withheld from Mr Maduro's government, but the company could avoid sanctions by recognizing Mr Guaidó.
Venezuela is heavily reliant on the US for its oil revenue - sending 41% of its oil exports there - while it remains in the top four crude oil suppliers to the US.
Maduro later announced he had told PDVSA to launch political and legal action, in US and international courts to protect its US subsidiary Citgo.
In Venezuela Guaidó says he is ordering Venezuela's Congress to name new heads of the PDVSA and Citgo, as he aims to take control of the country's assets
Mr Bolton and Mr Mnuchin said the sanctions were intended to prevent Mr Maduro's government from taking funds from the state oil company.
We have continued to expose the corruption of Maduro and his cronies and today's action ensures they can no longer loot the assets of the Venezuelan people, Mr Bolton said.
The US action blocks all PDVSA property and interests subject to US jurisdiction, and prohibits US citizens from engaging in transactions with them. But Mr Mnuchin said US-based subsidiary Citgo could continue operations if its earnings were deposited in a blocked account in the US.
Mr Bolton also urged Venezuela's military to accept the peaceful, democratic and constitutional transfer of power.
As Mr. Bolton was announcing the sanctions at a Washington news conference, observers spotted a handwritten message on his notepad. It read 5,000 troops to Colombia, though it is unclear what this means. Mr.Bolton declined at the press conference to rule out military involvement in Venezuela.
A White House spokesperson later said when asked about the note: As the President has said, all options are on the table.
The Maduro government has proven resilient, despite an economy in crisis, an already sharp contraction in oil production and other US efforts to isolate it. If countries such as China and Russia continue to support Venezuela, the government may be able to appeal to them for additional help.