Pope Francis (L) leaves at the end of a mass for Armenian Catholics marking 100 years since the mass killings of Armenians under the Ottoman Empire, on April 12, 2015 at St Peter's basilica in Vatican. Pope Francis faces a key diplomatic test today as he marks the centenary of the mass killings of Armenians and elects whether to use the word "genocide", at the risk of alienating Turkey. AFP PHOTO / ANDREAS SOLARO