WASHINGTON (AFP) -– U.S. president John F. Kennedy backed an American intermediary holding a secret meeting with Cuban President Fidel Castro just 17 days before his assassination in Dallas 40 years ago, according to a recently declassified audio tape.

Kennedy and his national security advisor, McGeorge Bundy, are heard discussing the possibility of a top-secret meeting with Castro in Havana, according to the tape released on Monday by the U.S. National Security Archive.

The tape reveals Bundy briefed Kennedy on Castro's invitation to a U.S. official at the UN, William Attwood, to come to Havana for secret talks that could have sparked improved relations with Washington.

The tape shows the ill-fated Kennedy's approval of the meeting, if official U.S. involvement could be plausibly denied.

"The documents show that JFK clearly wanted to change the framework of hostile U.S. relations with Cuba," said National Security Archive analyst Peter Kornbluh.

"His assassination, at the very moment this initiative was coming to fruition, leaves a major 'what if' in the ensuing history of the U.S. conflict with Cuba," Kornbluh said.

The Washington-based archive and research institute collects declassified public documents.