Raul Castro's daughter Mariela refused entry visa to Philadelphia to accept award for gay rights activism

Mariela Castron is director of Cuba's National Center for Sex Education (EPA)

The daughter of Cuban president Raul Castro has been refused permission to travel to Philadelphia, despite being invited to receive an award for her gay rights activism there.

Mariela Castro had been expected at a conference on civil rights for the LGBT communities sponsored by the Equality Forum next week.

The group's executive director Malcolm Lazin told the Associated Press: "We find it shocking that our State Department would deny freedom of speech, particularly at an international civil rights summit, to anyone, let alone the Cuban president's daughter."

Ms Castro was in New York yesterday as a UN-accredited expert attending meetings related to the UN population conference in Cairo in 1994. However, the Stae Department bans Cuban diplomats from travelling more than 25 miles from central Manhattan.

Ms Castro, 51, the niece of retired Cuban leader Fidel Castro, is director of the country's National Center for Sex Education and is Cuba's most prominent gay rights activist. She has instituted awareness campaigns, trained police on relations with the LGBT community and has lobbied politicians to legalise same-sex unions.

This year's Equality Forum event on LGBT rights is to focus on issues being faced within the community in Cuba, and Mr Lazin said Ms Castro had agreed to speak on a panel on 4 May before receiving an award for her activism at a dinner that night.

No visa problems were expected because she had been granted permission to attend an academic conference in California last year. However, a number of Cuban-American politicians had criticised the State Department for issuing an entry visa for that event, noting that US rules prohibit Communist Party members and other high-ranking Cuban government officials from entry without special dispensation.

Ms Castro has no official link to Cuba's communist government aside for her familial relations, although the sex education centre is part of the ministry for public health.

Ms Castro is yet to comment on her visa refusal and a State Department spokesman said he could not comment on individual cases.