US Southern Command chief Admiral Craig Faller made the remarks in Rio de Janeiro as the United States kicked off its annual UNITAS maritime exercise involving nine Latin American countries as well as the UK, Portugal and Japan.

"I won't speak to details of what we're planning and what we're doing, but we remain ready to implement policy decisions and we remain on the balls of our feet," Faller told reporters.

"The United States Navy is the most powerful navy in the world. If a policy decision is made to deploy the navy, I'm convinced that we'll be able to do what needs to be done."

His remarks came just weeks after President Donald Trump said he was considering a "blockade or quarantine" of the Latin American country.

Trump subsequently intensified sanctions on Venezuela this month, ordering a freeze on all government assets in the United States and barred transactions with its authorities.

Faller said US sanctions against Maduro's socialist regime were working and that the Venezuelan leader was isolated.

"The US government focus continues to be to place focused and targeted pressure on an illegitimate regime to ensure there's a transition to a legitimate, democratic government," Faller said.

"Part of that focus is to ensure that the right humanitarian assistance is allowed to get to the people who need it."

The United States is one of more than 50 countries to have recognized opposition leader Juan Guaido as interim president.

Oil-rich but cash-poor Venezuela is suffering one of the worst economic crises in its history, with a quarter of its 30 million population in need of aid, according to the United Nations.

Millions have fled, mostly to neighboring countries including Brazil.

UN rights chief Michelle Bachelet has criticized the latest US sanctions as "extremely broad" with the potential to exacerbate suffering among an already vulnerable population.

The two-week maritime operation off the coast of Brazil, involving more than 3,300 military personnel, "sends a message to Maduro and other partners that don't share the same values," Faller said.

"Naval exercises send a message to the world of what democracies that work together can do across a range of complex threats," he said.

Asked how he thought Maduro would react to the exercises, Faller said: "I don't know how Maduro looks at anything."