Mariela Castro Espin, daughter of Cuban President Raul Castro laughs while arriving at a medical lecture for health care providers on care for transgender patients at San Francisco General Hospital in San Francisco.

Fidel Castro's niece on Wednesday hailed Barack Obama's support for gay marriage and the loosening of US-Cuba travel restrictions, saying: “I would vote for President Obama.”

Mariela Castro, the daughter of President Raul Castro, also lamented the “small group of delinquents” whom she said were preventing the warming of ties between Washington and Havana.

“I think he's sincere and speaks from the heart,” Castro - whose US trip has been denounced by opposition Republicans - said of Obama's recent public endorsement of gay marriage.

“I think it's something that he truly believes in... If I were a US citizen, I would vote for President Obama,” she added, speaking via an interpreter at her first public event in a trip to San Francisco.

But Castro said US voters must press their government to completely “remove the economic and social blockades” that have characterised the US-Cuba relationship since her uncle Fidel seized power more than five decades ago.

“It's not fair - you can't allow a small group of delinquents to continue to manipulate and make it difficult for the US and Cuba to have a relationship,” she told about 200 people gathered at a local gay rights centre.

“We have a lot in common,” Castro, wearing a purple scarf and flanked by several nervous bodyguards, said. “Don't let them pull us apart.”

Castro, in town for an academic conference on Latin America, has been a staunch advocate for gay and transgender Cubans.

The 50-year-old trained sexologist is credited with helping to push through reforms in the Communist country, such as health plan coverage for sex-change operations.

Castro said the legal reforms were successful largely because her father and uncle have backed her work. The men were won over by her late mother, who also cared deeply about gay and transgender rights, she said.

Castro's visit to the United States, although not her first, has predictably stirred up controversy in a country that has had little contact with the island nation since her uncle came into power in a Communist revolution in 1959.

Republican presidential candidate Mitt Romney released a statement criticising the Obama administration for “welcoming the daughter of a dictator.”

Castro did not directly address the criticism surrounding her visit but said she was “lucky that the US government stood by its laws and granted me a visa.”

Despite the visa approval for Castro, at least a dozen other Cuban scholars who had hoped to attend the same conference - sponsored by the Latin American Studies Association - were denied entry by the US government.

University of Havana professor Esteban Morales, whose research focuses on racial issues in Cuba, said he learned Monday his visa application was among those rejected.

In an email, Morales said he believes his visa denial was a result of the US government caving to pressure from hardline groups that oppose normalised US-Cuba relations.

He has visited the US nearly four dozen times for academic reasons, he said.

“It's truly stupid to have denied my visa this time,” he wrote. “I don't believe there is any reason for the denial, beyond political manipulation.”

Last week, the US State Department said it had granted most of the 77 Cuban visa applications for the conference and could not comment on specific cases.

Castro was scheduled to lead a Thursday morning panel on sexual politics at the San Francisco conference. Next week, she will visit the New York Public Library for a conversation on international gay rights.

“In the few days I've been here, I've learned a lot from you,” she told the American crowd. “And I feel really good to be with you.” - AFP