"Please join me in praying for the victims of the ferry disaster in Korea and their families," Francis said in a tweet published on his Twitter account @pontifex.
Francis is due to make a five-day visit in August to South Korea, which has more than five million Catholics -- around 10 percent of the population.
He will be the first pope to visit Asia since John Paul II. His predecessor Benedict XVI did not travel there during his eight-year pontificate. (AFP)