US Secretary of State Marco Rubio has said Cuba poses a “national security threat” to the United States, warning that the chances of reaching a peaceful agreement with Havana are “not high”.

Speaking to reporters on Thursday, Rubio said Washington still preferred diplomacy but suggested progress with the Cuban government remained unlikely.

“I'm just being honest with you, you know, the likelihood of that happening, given who we're dealing with right now, is not high,” Rubio said.

The comments came a day after the US charged former Cuban president Raul Castro with murder over the 1996 downing of two aircraft that killed US nationals.

Rubio also accused Cuba of being “one of the leading sponsors of terrorism in the entire region”, claims strongly rejected by Bruno Rodriguez Parrilla.

Rodriguez accused Rubio of spreading “lies” and attempting to “instigate a military aggression” against the island.

The latest exchange marks another sharp escalation in tensions between the US and Cuba as the island faces severe fuel shortages, blackouts and food scarcity during an ongoing economic crisis.

President Donald Trump also commented on the situation, calling Cuba a “failed country” and suggesting his administration could achieve what previous US presidents could not.