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 Maduro have increased in recent days.
The US and more than 20 countries have recognised 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 recognising 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.
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Bolton and 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," 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.
Bolton also urged Venezuela's military to "accept the peaceful, democratic and constitutional transfer of power".
As 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.
One observer suggested the apparent gaff may be an infringement of operational security.
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."
However, one US official anonymously told AFP news agency "we are not seeing anything that would support" a possible troop deployment to Colombia.
Earlier in the day a state television broadcast showed Maduro welcoming home diplomats recalled from Washington DC.
Venezuela broke off relations with the US last week in response
to its recognition of Guaidó as interim leader and ordered all US diplomats to leave the country.
However, on Saturday Venezuela's foreign minister announced it would allow 30 days for the two sides to set up "interest offices" in each others' countries.