"I did not know the phrase I used in Miami today was associated with Che Guevara & I did not mean to offend anyone who heard it that way," de Blasio tweeted.
National security adviser Walt Whitman Rostow called the execution "stupid" in a memo to President Lyndon B. Johnson.
After years of silence, a former CIA operative speaks out about Castro, Oswald and the assassination of JFK.
Negotiations between the two sides are continuing in the Cuban capital of Havana.
Bogota agrees compensation deal with rebels for victims of a decades-long civil war.