Cuba has suspended all postal deliveries to the United States until further notice.The suspension follows the introduction of stricter security measures by the US last year after the attempted mailing of explosives from Yemen.
The Cuban postal service says large amounts of mail were refused entry and returned in the following months.
Correspondents say the cost of so many returns may have led to the decision to stop the service.
Postal service between the US and Cuba had been suspended for 42 years after Cuba's communist revolution, and only resumed in 2009 via third countries.
President Barack Obama's decision to renew the service was widely seen as a move towards repairing relations between the two countries.
Its suspension is likely to be interpreted as a setback to the president's efforts at easing tension and improving people-to-people ties between Cuba and the US.
The US tightened its security on air cargo after bombs hidden in cartridges were intercepted on route from Yemen to the US in cargo planes.