Pope Francis, who played a key role in the diplomatic thaw between Washington and Havana, will visit Cuba in September after a scheduled visit to the US, the Vatican confirmed on Wednesday.

His visit to the island that has many Roman Catholics will be the third by a pope after Jean Paul II in 1998 and Benedict XVI in 2012.

The Holy See has said that the 78-year-old pontiff personally mediated between the US and Cuba with the Vatican hosting delegations from the two countries in October.

Secret negotiations then led to the surprising announcement in December 2014 that Washington and Havana would seek to restore diplomatic ties.

Pope Francis is already scheduled to visit the US in late September.

The leader of the world's Roman Catholics confirmed late last year that he would visit the US to take part in a Catholic Church congress in Philadelphia.

During the trip, he is also scheduled to speak before the United Nations in New York, become the first pontiff to address the US Congress and to meet with US President Barack Obama at the White House.