Havana: Cuban revolutionary leader Fidel Castro broke his silence on US President Barack Obama's recent trip to Cuba, saying he brought "sweetened words", but little of substance, the media reported on Tuesday. In a kind of open letter to Obama, published on Monday in state-run daily Granma, Castro said that he had "the elemental duty to respond to Obama's speech" to the Cuban people, delivered during his March 20-22 visit, Xinhua reported. "Obama made a speech in which he used the most sweetened words to express: 'It is time, now, to forget the past, leave the past behind, let us look to the future together, a future of hope.'" said Castro. "And it won't be easy; there will be challenges and we must give it time; but my stay here gives me more hope in what we can do together as friends, as family, as neighbours, together," Obama told the Cuban audience in his speech. While Obama's speech marked a radical change in the rhetoric usually directed at Cuba by the US, it failed to address any of the country's major grievances, Castro noted. "I suppose all of us were at risk of a heart attack upon hearing these words from the president of the US. After a ruthless blockade that has lasted almost 60 years, and what about those who have died in the mercenary attacks on Cuban ships and ports, an airliner full of passengers blown up in midair, mercenary invasions, multiple acts of violence and coercion?" said the former Cuban leader. A Cuban airliner from Barbados to Jamaica was blown up on October 6, 1976 by a terrorist bomb attack. All 73 people on board were killed. Cuba has accused the US of being an accomplice of the attack. Cuba does not need the US for its development, said Castro, noting that the Caribbean country has made significant progress in education, science, health and other fields despite the naval blockades, sanctions and punitive measures Washington imposed on the island for half a century. "We are capable of producing the food and materials we need with the efforts and intelligence of our people. We do not need the empire to give us anything," said Castro. To highlight the similarities between the two nations, Obama said: "Cuba, like the US, was built in part by slaves brought here from Africa. Like the US, the Cuban people can trace their heritage to both slaves and slave-owners." But Castro stressed that Cuban socialism has made more headway in eradicating racial discrimination than the US has through its liberal democracy. "The revolution swept away racial discrimination," said Castro, adding that "the hateful, racist bourgeois custom of hiring strongmen to expel black citizens from recreational centres was swept away by the Cuban Revolution." Castro led the 1959 Cuban Revolution that toppled the US-backed dictatorship. He had governed the country till 2006, when his health deteriorated, and was succeeded by his brother Raul Castro.