US President Donald Trump on Thursday warned of possible military intervention in Cuba, as Secretary of State Marco Rubio declared that Cuba has been a national security threat for years. 

Trump said previous US presidents have considered intervening in Cuba for decades but that 'it looks like I´ll be the one that does it.'

'Other presidents have looked at this for 50, 60 years, doing something,' Trump told reporters when asked about Cuba during an environmental event in the Oval Office. 

'And, it looks like I´ll be the one that does it. So, I would be happy to do it.'

Secretary of State Marco Rubio told reporters separately that Cuba has been a national security threat for years because of its ties to US adversaries such as Russia and China and that Trump is intent on addressing it.

Rubio, the son of Cuban immigrants who has long taken a hard-line against Cuba´s socialist leadership, said the Trump administration wants to resolve differences with Cuba peacefully but is doubtful the US can reach a diplomatic resolution with the island's current government.

Trump's 'preference is always a negotiated agreement that´s peaceful. That´s always our preference. That remains our preference with Cuba,' Rubio said in Miami before boarding a plane to attend a NATO meeting in Sweden and then visit India.

'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,' he said.

Top Trump aides - including Rubio, CIA chief John Ratcliffe and other senior national security officials - have met with Cuban officials in recent months to explore possible improvements in relations. But the U.S. side has come away unimpressed from those talks, leading to even more sanctions imposed on the Cuban government in the past week.

Over the years, Cuba has gotten used to 'buying time and waiting us out,' Rubio said. 'They´re not going to be able to wait us out or buy time. We´re very serious, we´re very focused.'

When asked whether the US would use force in Cuba to change the island's political system, Rubio repeated that a diplomatic settlement was preferred but noted that 'the president always has the option to do whatever it takes to support and protect the national interest.'

He pushed back on a reporter´s suggestion that it sounded like 'nation-building,' insisting it was about addressing a national security risk.

The renewed threat takes on greater weight a day after the administration announced criminal charges against the island's former leader, Raúl Castro. 

 Federal prosecutors on Wednesday unveiled an indictment that accuses Castro of ordering the shootdown in 1996 of civilian planes flown by Miami-based exiles. The charges, which were secretly filed by a grand jury in April, included murder and destruction of an airplane.