The warning came amid reports of armed militias.
Deposed Venezuelan President Nicolás Maduro and his wife appeared in a federal court in New York City on Monday, following their capture by U.S. forces over the weekend in a military operation in the Venezuelan capital of Caracas.
Following the operation, President Donald Trump said that the U.S. would "run" Venezuela for an unspecified "period of time."
Venezuelan Vice President Delcy Rodriguez has been sworn in as interim leader to lead the country after what the Venezuelan Supreme Court described as Maduro's "kidnapping."
Nicolas Maduro's wife Cilia Flores, is also in U.S. custody in New York, sources familiar with the matter said.
Shortly before 9 p.m., Maduro was on his way to the Metropolitan Detention Center, Brooklyn, where he will be held.
-ABC News' Aaron Katersky, Luke Barr and Katherine Faulders
Photos and videos appeared to show Maduro being escorted by agents from a plane after it landed outside New York City.
Maduro was expected to be flown into the city by helicopter and expected to be processed on federal charges and detained in a federal jail as he awaits trial.
Democratic National Committee chair Ken Martin criticized the U.S. operations in Venezuela in a statement on Saturday, excoriating Trump for what Martin called "unconstitutional and illegal strikes."
"Today, Trump finally said the quiet part out loud. The justification for this war isn’t about stemming the flow of drugs. This is about regime change. This is about enriching oil corporations and billionaires," Martin said.
He called for Congress to "immediately assert its constitutional authority" over U.S. military moves.
"This is the worst kind of betrayal from Trump. He committed the United States to an uncertain role in South America with an indeterminate timeline," Martin said.
-ABC News' Oren Oppenheim
Some protests were reported in the U.S. and other countries following the attack.
In New York City's Times Square, crowds mustered with signs urging the U.S. to stay out of Venezuela.
A similar crowd also demonstrated outside of the White House.
Meanwhile, in Doral in South Florida, home to the largest Venezuelan community in the U.S., people gathered in the street to cheer Maduro's capture, dancing and waving Venezuelan flags.
Elsewhere around the world, protesters in Paris burned the American flag and waved "boycott the U.S." signs. Demonstrators in Athens also burned American flags.
In Colombia, protesters demonstrated in front of the U.S. embassy while in In Buenos Aires, a banner was tacked up reading "Trump, your drug is oil."
-ABC News' Victoria Beaulé
