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.

Mr Bolton also sent a strong warning to President Daniel Ortega of Nicaragua, where more than 300 people have been killed since protests erupted in April calling for Mr Ortega’s resignation.

"Free, fair, and early elections must be held in Nicaragua, and democracy must be restored to the Nicaraguan people," he said.

"Until then, the Nicaraguan regime, like Venezuela and Cuba, will feel the full weight of America’s robust sanctions regime."

Mr Bolton, who was George W Bush’s ambassador to the UN when the term "axis of evil" was coined, said the "troika of tyranny" must be stopped.

"This troika of tyranny, this triangle of terror stretching from Havana to Caracas to Managua, is the cause of immense human suffering, the impetus of enormous regional instability, and the genesis of a sordid cradle of communism in the Western Hemisphere," he said.

He mocked Miguel Diaz-Canel, the Cuban president; Nicolas Maduro, Venezuela’s leader, and Mr Ortega.

"These tyrants fancy themselves strongmen and revolutionaries, icons and luminaries," he said.

"In reality, they are clownish, pitiful figures more akin to Larry, Curly, and Moe."

Mr Bolton then went on to call Brazil’s president-elect, Jair Bolsonaro, a "likeminded leader" and said his election last weekend demonstrates "a growing regional commitment to free-market principles, and open, transparent, and accountable governance."

Mr Bolsonaro, whose victory moved Brazil sharply to the right, built his popularity on a mixture of often outrageous comments and hard-line positions, but he consolidated his lead by promising to enact market-friendly reforms.

His election has sparked grave concerns among human rights activists in the country, and fears of a slide back towards Brazil’s repressive recent history.

Mr Bolton, however, welcomed his election, saying it was one of several "positive signs for the future of the region".