Iran's foreign minister on Sunday warned the US against deploying its navy in the Caribbean to disrupt Iranian fuel shipments to Venezuela.

In a letter to United Nations chief Antonio Guterres, Mohammad Javad Zarif warned against "America's movements in deploying its navy to the Caribbean in order to intervene and create disruption in (the) transfer of Iran's fuel to Venezuela."

He said that any such action would be "illegal and a form of piracy," according to a foreign ministry statement.

Zarif added that the US would be responsible for "the consequences of any illegal measure."

Iran's Fars News claimed Saturday that it had received information that four US Navy warships are in the Caribbean for a "possible confrontation with Iran's tankers."

Elliot Abrams, the State Department's Venezuela envoy, has alleged that Caracas is paying Iran in gold to restore its troubled oil sector.

The US has imposed unilateral sanctions aimed at ending oil exports by both Iran and Venezuela, both major crude producers.

Zarif's deputy has summoned the Swiss ambassador, who represents Washington's interests in Tehran, to communicate Iran's "serious warning".

Abbas Araghchi said any potential threat to Iran's tankers would be met with a "quick and decisive response."

Venezuela has the world's largest proven oil reserves but analysts say that the sector operates below capacity.

The country's economy is in a state of collapse, with millions fleeing as they lack basic goods.

Iran has also taken a hit from renewed US sanctions after US President Donald Trump pulled out of a nuclear accord in 2018.

Maduro has withstood more than a year of US-led efforts to remove him and retains the support of the military.

Iran has repeatedly expressed support for Maduro against opposition leader Juan Guaido, who is recognised by some 60 nations as interim president due to reports of irregularities in Maduro's 2018 re-election.