Cuban President Raul Castro on Sunday arrived at the Vatican for a "strictly private" meeting with Pope Francis.

Castro was due to thank the pontiff -- the first South American pope -- for his key role in brokering the rapprochement between Havana and Washington.

He played a key role in the secret negotiations between the United States and Cuba that led to the surprise announcement in December that they would seek to restore diplomatic ties after more than 50 years of tensions.