U.S. sanctions Cuba's Raul Castro, members of his family

The Trump administration on Thursday imposed diplomatic sanctions on Cuban Communist Party Leader Raul Castro, accusing him of "gross violations of human rights" as it sought to step up pressure on Havana over its support of Venezuela's socialist president, Nicolas Maduro.

In President Donald Trump's toughest direct action against Cuba's leadership since taking office in 2017, the U.S. targeted Castro, Cuba's former president and brother of the late Fidel Castro, as well as family members.

"Castro is responsible for Cuba's actions to prop up the former Maduro regime in Venezuela through violence, intimidation, and repression," Secretary of State Mike Pompeo said in a statement, reiterating the administration's position that Maduro is no longer the legitimate president.

The sanctions will block Castro and his immediate family from entering the United States, Pompeo said.TheState Department also sanctioned his children, Alejandro Castro Espin, Deborah Castro Espin, Mariela Castro Espin, and Nilsa Castro Espin.

Pompeoalsoaccused Castro, who is considered Cuba's most powerful figure, of overseeing "a system that arbitrarily detains thousands of Cubans and currently holds more than 100 political prisoners."

The government in Havana, which is officially led by President Miguel Diaz-Canel, did not immediately respond to a request for comment, but Diaz-Canel on social media earlier this week criticized what he called American "persecution" of Cuba and Venezuela.

It was the latest in a series of punitive measures that the U.S. administration has taken against Washington's old Cold War foe, steadily rolling back the historic opening to Havana under Trump's Democratic predecessor, Barack Obama.

Trump has focused especially on Cuba's support for Maduro. Earlier this year, the United States and dozens of other countries recognized opposition leader Juan Guaido as Venezuela's legitimate president, accusing Maduro of rigging the country's last election.

"In concert with Maduro's military and intelligence officers, members of the Cuban security forces have been involved in gross human rights violations and abuses in Venezuela, including torture," Pompeo said.

Last week, the United States expelled two of Cuba's United Nations diplomats, citing "influence operations."

Washington has made it clear that a key objective of its pressure campaign is to force Cuba to abandon Maduro, something Havana has said it will never do.

Trump has stopped short of breaking off diplomatic relations with Cuba restored by Obama in 2015 after more than five decades of hostility.

Maduro and his loyalists have accused Guaido, who earlier this year assumed an interim presidency to rival Maduro's government, of trying to mount a U.S.-directed coup.

Pompeo said, "Castro is complicit in undermining Venezuela's democracy and triggering the hemisphere's largest humanitarian crisis, forcing 15 per cent of the Venezuelan population to flee the country and precipitating a food shortage and health crisis of unprecedented scale in this region."