Former US Secretary of State Henry Kissinger pushed for a military invasion of Cuba in the mid-1970s, newly released declassified documents show.

He also said he would "smash" Fidel Castro for sending troops to Angola.

The material, made public by the National Security Archive, uncover candid conversations between Mr Kissinger and US president Gerald Ford in 1976 after Cuban troops were deployed in Angola to support independence fighters, sparking fears in Washington of growing communist influence in Africa.

"I think we are going to have to smash Castro," Mr Kissinger told Ford, adding that they would have to wait until after Cuba's upcoming election.

"I agree," Mr Ford replied.

Mr Kissinger said a military response would have to be in earnest and vowed not to use "halfway measures," particularly if Cuban troops moved into other southern African nations.

"If we decide to use military power it must succeed. There should be no halfway measures," he said.

"If they move into Namibia or Rhodesia, I would be in favor of clobbering them."

He took a stab at president Mr Castro too, calling the late leader a "pipsqueak" for his military support in Angola, as he vowed to "crack the Cubans."

The previously classified documents - 116 pages in total - also show that the angry turn in US relations with Cuba followed an earlier attempt by Kissinger to mend ties with Havana.

Mr Kissinger sent two envoys to New York's La Guardia airport in January 1975 for a meeting with Cuban emissaries to normalize relations between the Cold war foes.

The documents are published in a book called "Back Channel to Cuba: The Hidden History of Negotiations Between Washington and Havana."