HAVANA (AFP) - Cuba on Tuesday offered its "unconditional support" to Venezuela after US President Barack Obama authorised new sanctions against senior officials of the South American oil producer, Havana's closest ally.

An official statement published in the island's state-run media called Obama's executive order implementing the sanctions "arbitrary and aggressive."

"Cuba again reiterates its unconditional support and that of our people for the Bolivarian Revolution, the legitimate government of President Nicolas Maduro, and the heroic brotherly people of Venezuela," the statement said.

The Cuban reaction marked its first public confrontation with the United States since the two countries began discussions in December on fully restoring diplomatic relations.

In Caracas, meanwhile, President Nicolas Maduro, who recalled his envoy to Washington, denounced the US action as "the most aggressive, unjust and harmful blow against Venezuela."

In activating the sanctions, Obama called the situation in Venezuela "an extraordinary threat to the national security" of the United States.

The sanctions targeted Venezuelan officials who the United States said were linked to human rights abuses, including a crackdown on anti-government protests last year that left 43 people dead.

"No one has the right to intervene in the internal affairs of a sovereign state or to declare, without foundation, someone a threat to national security," Cuba said.

It said the US measures were "in reprisal for the measures adopted (by Venezuela) in defense of its sovereignty in the face of meddling acts by the governmental authorities and Congress of the United States."

Cuban leader Fidel Castro congratulated Maduro on his "brilliant and brave" stance against the US in a letter also published Tuesday by the Cuban press.

"Your words will go down in history as proof that humanity can and must know the truth," Castro wrote.