U.S. hostile foreign policy towards Cuba in the past half a century has been a failure, a Cuban political observer and diplomat has said.

Cuba has withstood the U.S. web of sanctions for decades despite undergoing sea changes such as the death of its long-time leader Fidel Castro, said Carlos Alzugaray, 77, a veteran diplomat and political scientist specializing in U.S.-Cuba ties.

"They also thought the death of Fidel Castro (in November 2016) would be a moment of weakness, but it was not," he said.

"And the same thing happened with the presidential transition from Raul Castro to Miguel Diaz-Canel," said Alzugaray, co-president of the Cuba section of the Latin American Studies Association based in the U.S. state of Pennsylvania.

The long-running trade embargo against Cuba, imposed by a presidential decree of then U.S. President John F. Kennedy in February 1962, has no legal basis and its legality is debatable even according to U.S. laws, the observer said.

"Today it is a very complex network of sanctions that were consolidated and codified in the 1990s" through various laws, including the Torricelli Act, Helms-Burton Act and others, he said.

The Torricelli and Helms-Burton acts, which were passed in 1992 and 1996 respectively, consolidated the U.S. sanctions into law, and also put in the hands of U.S. Congress the possibility of lifting the embargo, a power that was initially a presidential prerogative.

Lifting the embargo has now become much more complex since it has to be approved by a bipartisan Congress, said Alzugaray. "Eventually it could happen that one day they realize the embargo makes no sense, but both Democrats and Republicans would have to agree," he said.

In Cuba, the embargo is more commonly referred to as a blockade, because it effectively blocks other countries from doing business with the island and strangles its economy. Calling it an embargo is "just a euphemism," said the author of three books, and scores of essays and articles on the relations between Washington and Havana.

"In technical terms, (an embargo) is when a country decides not to trade with another, which only prevents direct exchange. But in Cuba's case, there is a set of economic and financial sanctions that transcend trade," and impact third countries, said Alzugaray.

The blockade has an extraterritorial aspect, because the United States demands that subsidiaries of U.S. companies in third countries not trade with Cuba, "which is an extraterritorial application of U.S. law," he said.

At present, Cuba cannot buy on the international market goods that have more than 10 percent U.S. components. At the same time, it cannot export merchandise with more than 10 percent Cuban parts to the United States.

As the current administration of U.S. President Donald Trump seeks regime change in Cuba, the blockade not only continues, but has been intensified, to the detriment of the Cuban people, he added.