Last week, the grandson of former Cuban leader Raul Castro - Raul Guillermo Rodriguez Castro - asked a wealthy Havana businessman to deliver a personal secret letter to US President Donald Trump, bypassing the usual diplomatic channels.
This was reported by The Wall Street Journal, citing US officials.
The letter was formatted as a diplomatic note and bore an official Cuban seal.
The message to Trump offered economic and investment agreements, as well as easing sanctions.
The US representative added that the letter also warned that "the Cuban regime is preparing for a US invasion".
The letter was entrusted to Cuban businessman Roberto Carlos Chamiso Gonzalez, who was supposed to deliver it personally to the White House.
The courier was stopped at the Miami airport by US Customs and Border Protection agents, who seized the document and returned the businessman to Cuba.
Analysts see this act as an extraordinary attempt by Havana to establish direct contact with Trump, bypassing Secretary of State Marco Rubio, who is known for his hard line towards the Cuban government.
According to publications in The Wall Street Journal and The Telegraph, this move comes at a time of severe economic crisis in Cuba and rumors of secret negotiations about the future of the island.