Venezuela and Cuba were hit with further sanctions by the United States on Thursday, as Donald Trump's hawkish national security adviser unveiled a new policy on countries he termed, with Nicaragua, as "the troika of tyranny".

Speaking at the Freedom Tower in Miami, at the heart of the city's Cuban-American and Venezuelan dissident communities, John Bolton said the policy showed the US "will no longer appease dictators and despots near our shores in this hemisphere."

Venezuela will, under the new policy, be unable to sell its gold. Much of the country's reserves have been shipped to Turkey in the last year, with over $870 million exported. Mr Trump reportedly asked his staff last summer why the US could not invade Venezuela and oust the country's leadership.

Cuba, in turn, faces a series of new sanctions against entities linked to the military and intelligence services, which control much of the country. The new sanctions build upon foundations laid by Mr Trump in June 2017.

Both sets of sanctions are designed to make doing business in the countries harder, and punish their socialist leaders.