Relations between Cuba and the US are being pushed to breaking point by a bizarre spat that began with an electronic sign fixed to the side of the US mission in Havana.

The five-foot high ticker, which is spread across 25 windows of the mission's fifth floor, is broadcasting a constant stream of quotes from human rights and anti-communist leaders. Its inaugural message, "I have a dream that one day this nation will rise up", from Martin Luther King Jnr's 1963 speech, appeared in crimson text on January 16.