US President Donald Trump said it would be "smart" for his Venezuelan counterpart, Nicolas Maduro, to step down as US naval forces pressed a blockade on the South American country's oil wealth.

Venezuela's key ally Moscow has expressed its "full support" for Maduro's government as Washington has dialed up military operations and threats against Caracas.

Asked on Monday at his Florida home if Washington's threats were designed to force Maduro to leave office after 12 years, Trump said: "That's up to him, what he wants to do. I think it would be smart for him to do that."

But he added: "If he wants to do something – if he plays tough, it'll be the last time he's ever able to play tough."

Firing back just hours later, Maduro said Trump would be "better off" if he focused on his own country's problems rather than threatening Caracas.

"He would be better off in his own country on economic and social issues, and he would be better off in the world if he took care of his country's affairs," Maduro said in a speech broadcast on public television.

The pledge from Moscow, which is embroiled in the war in Ukraine, came on the eve of a UN Security Council meeting on Tuesday to discuss the mounting crisis.

In a phone call, foreign ministers of the allied nations blasted the US actions, which have included strikes on alleged drug-trafficking boats and the seizure of two oil tankers. A third ship was being pursued, a US official said on Sunday.

"The ministers expressed their deep concern over the escalation of Washington's actions in the Caribbean Sea, which could have serious consequences for the region and threaten international shipping," the Russian foreign ministry said of the call between Sergei Lavrov and Venezuelan counterpart Yvan Gil.

"The Russian side reaffirmed its full support for and solidarity with the Venezuelan leadership and people in the current context," it added in a statement.

Trump claims Caracas under Maduro is using oil money to finance "drug terrorism, human trafficking, murder and kidnapping."

He has also accused Venezuela of taking "all of our oil" – in an apparent reference to the country's nationalisation of the petroleum sector, and said: "we want it back."

Caracas, in turn, fears Washington is seeking regime change, and has accused Washington of "international piracy."

Russia and China backed Caracas's request for the UN Security Council meeting to discuss "the ongoing US aggression". (AFP)