Francis gave the authorisation a day earlier, the Vatican said, paving the way for the 124 martyrs to be beatified in a solemn ceremony. Beatification is the last formal step before sainthood in the Catholic church.
The martyrs were killed "out of hatred to the faith in Korea," the Vatican said.
Last month, the Vatican said a papal trip to South Korea in August was under consideration. The development about the beatification makes a pilgrimage by Francis there "increasingly likely," said AsiaNews, a Vatican-affiliated missionary news agency.
Francis has made reconciliation a theme of his nearly year-old papacy.
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Catholics in Asia have long been a minority, with the Philippines the most notable exception. But the Vatican sees the Asia continent as a place for strong growth.
Today, the pontiff was invited to visit Sri Lanka. Meeting with a group of Sri Lankan Catholics at the Vatican, Francis referred to that country's quarter-century of civil war when he told his audience that "many tears have been shed in recent years, on account of the internal conflict which caused so many victims and so much damage."
Sri Lanka's cardinal, Albert Malcolm Ranjith Patabendige Don, took the occasion to invite Francis to his homeland. Francis thanked him, saying "I take up this invitation, and I believe that the Lord will give us the grace" to make the trip happen, the Italian news agency ANSA reported.
The pope's only officially scheduled trip this year is a three-day pilgrimage in late May to Jordan, Israel and the West Bank.