At the end of a mass in Cuba, where the Marxist rebels and the Colombian government have been holding talks, the Argentine-born pontiff called on the two sides to seize the opportunity and strike a peace deal.

"We do not have the right to allow ourselves yet another failure," Pope Francis said. "May the blood shed by thousands of innocent people during long decades of armed conflict … sustain all the efforts being made, including those on this beautiful island, to achieve definitive reconciliation," the Pope said in his Angelus address at Havana's Revolution Square.

The Revolutionary Armed Forces of Colombia (FARC) said in a statement that the Pope's appeal "strengthens" the peace process.

FARC, which emerged in the mid 20th century in Colombia to battle rural poverty, has fought a dozen Colombian governments since its inception. The five-decades-long conflict – South America's longest - has killed more than 200,000 people.

A US-backed offensive has weakened the rebel group substantially over the past 10 years. FARC and Bogota have been engaged in peace talks for nearly three years now.

Earlier, Francis also urged the communist government of Cuba and the United States to continue on the path of reconciliation. The Pope had facilitated talks between the Washington and Havana last year.

The discussions led to a prisoner exchange, the reopening of embassies and the easing of some travel and trade restrictions. A continuing US economic embargo can only be removed by a vote in the US Congress.

Pope Francis has arrived in Cuba at the start of a nine-day tour of the Caribbean island and the United States. He used his arrival speech in Havana to praise restored relations between the two former Cold War foes.

shs/sgb (AP, AFP)