US President Barack Obama has started an extraordinary visit to Cuba, eager to push decades of acrimony deeper into the past and forge irreversible ties with America's former adversary.

Pope Francis has hailed the detente between the US and Cuba as a model of reconciliation for the world.

A pair of heavily armed Cuban soldiers seized a city bus, killed an army officer and triggered a gun battle in a foiled bid to hijack a charter flight bound for the US.

A Cuban plane hijacked by a man who said he had two grenades today took again from a Havana airport after a night of tense negotiations.