Barack Obama's historic policy shift toward Cuba would be short-lived under a Marco Rubio presidency, the Florida senator has told the Guardian, one week after the White House made the final major step in renewing diplomatic ties with the Castro regime.

Rubio, a top contender for the Republican nomination for president, said he would "absolutely" reverse the unilateral steps Obama has taken thus far to normalize relations between the two countries – including closing down the embassies that are slated to open on 20 July – if he is elected to the White House in 2016.

"In fact, I think they're in violation of the law," Rubio said during an interview at the tail end of a three-day campaign swing through Iowa. "The statute passed by Congress specifically prohibits many of the things he [Obama]'s now undertaking. It says those things can only happen after certain conditions have been met, none of which have been met. As president, I will follow the law."

Rubio, the son of Cuban immigrants, has been the leading opponent in the US Congress of Obama's overtures to the island nation.

Ever since the president announced in December that the US would end a half-century diplomatic freeze with Cuba, Rubio has publicly castigated the administration at every turn – be it the lifting of certain commercial and travel sanctions, the removal of Cuba from a list of state sponsors of terrorism, and Obama's announcement last week on the reopening of embassies between Washington and Havana.

US and Cuban embassies to re-open: 'This is what change looks like'

In addition to saying he would reverse those steps, Rubio also defended his steadfast opposition to lifting the 50-year-old US trade embargo on Cuba – which critics argue has taken a significant humanitarian toll on the Cuban people while doing little to deter the grip on power of the Castro brothers.