Pope Francis has said it is as if the world is living through a third world war.
The Pope, within an hour of landing in Cuba at the start of his three-day visit, issued a call for prayer in "these times which are like those of a third world war."
His words, a departure from his prepared speech, echoed the concerns he raised when he spoke to journalists on the 12-hour flight from Rome, as has become his norm on foreign trips. La Repubblica reported that he said: "I believe that the world is thirsty for peace". He told press on the flight of his anxieties about "wars, migrants, and the wave of people that are fleeing wars and fleeing death."
Pope Francis was instrumental in the dialogue that led to the restoration of diplomatic relations between Cuba and the United States earlier this year.
On arrival in the communist and former atheist country he said: "For some months now, we have witnessed an event which fills us with hope: the process of normalising relations between two peoples following years of estrangement. It is a sign of the victory of the culture of encounter and dialogue, the system of universal growth over the forever-dead system of groups and dynasties.
"I urge political leaders to persevere on this path and to develop all its potentialities as a proof of the high service which they are called to carry out on behalf of the peace and well-being of their peoples, of all America, and as an example of reconciliation for the entire world."
He also appeared to make a veiled reference to the dissidents and political activists imprisoned by the regime when he said he hoped his greeting would "embrace especially all those who, for various reasons, I will not be able to meet."
The Pope's visit to Cuba coincides with the centenary of Pope Benedict XV's declaration of our Lady of Charity of El Cobre as Patroness of Cuba. Pope Francis said: "The growing devotion to the Virgin is a visible testimony of her presence in the soul of the Cuban people."
He was greeted at the airport by Archbishop of Havana Cardinal Jaime Ortega and Cuban president Raúl Castro.
Earlier, US President Barack Obama telephoned President Castro to talk about the recent restoration of diplomatic ties and the reopening of embassies, recognising the role played by the Pope.
In his own welcoming address to Pope Francis, President Castro acknowledged the importance of the reestablishment of diplomatic relations but said this was just a first step. He called for an end to the US embargo, or blockade, which he said "causes human and personal harm, is immoral and illegal. It needs to end." He also called for the US to return the "territory usurped by the Guantanamo Naval Base."