Criticising what he called the "diplomacy with dictators" being undertaken by US President Barack Obama, Republican presidential aspirant and Florida Senator Marco Rubio has pledged to reverse the administration's "weak" policy towards Iran and Cuba.

In an opinion article published on FOX News, Rubio maintained that both Iran and Cuba continue to pose threats to the US.

The Republican senator said the Shia leadership in Iran, which reached a nuclear agreement with the US and other major powers recently, still aspire to have "cataclysmic showdown with the West" in the future.

Rubio also accused Cuba of continuing to work with Russia and China to spy on the US, and of harbouring fugitives from American justice.

"Centuries of global affairs tell us the best way to affect an outcome with volatile leaders is through strength and example, while the worst is through weakness and concession. Yet weakness and concession are the preferred tools of statecraft for this administration," Rubio said of the Obama administration.

If he becomes the next US president, Rubio vowed to "roll back" Obama's deal with Iran, and "concessions" to the regime of Marxist Cuban political leader Fidel Castro.

The Republican presidential hopeful said he will immediately re-impose sanctions on Iran if he wins the White House.

"I will give the mullahs a choice: either you have an economy or you have a nuclear programme, but you cannot have both. I will also ask Congress to pass crushing new measures that target human rights abuses and the sponsorship of terrorism," Rubio said.

He also said he will make sure that US forces in the Middle East "are positioned to signal readiness and restore a credible military option."

Rubio further said he plans to pressure Castro's regime to stop human rights violations, and to place Cuba again on the state sponsor of terror list.

"These are the actions required to restore the safety and security President Obama has cost us through his diplomacy with dictators. When it comes to the challenges posed by Iran and Cuba, our task is straightforward – we must prevent Iran from gaining a nuclear weapon and we must guarantee that the United States stands on the Cuban people, not their oppressors," Rubio said.