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Reuters
Pope Francis has expressed hope his visit to the Republic of Ireland will "further the growth of unity and reconciliation" among all Christians.
In a video message to mark the start of the World Meeting of Families, he said he was "excited at the thought of returning to Ireland".
Pope Francis' 36-hour visit begins on Saturday and coincides with the global gathering of the Catholic Church.
Catholic cathedrals marked the launch by ringing bells on Tuesday evening.
The World Meeting of Families is held every three years, with thousands of people from across the world attending.
It is the first time the event has been held in Ireland.
'Irish family'
In his message, the pontiff sent a "warm word of greeting to all the Irish people".
"Although the specific reason for my visit to Ireland is the World Meeting of Families, I would like to include all the members of the Irish family," he said.
"In a particular way, I pray that it may further the growth of unity and reconciliation among all Christ's followers, as a sign of that lasting peace which is God's dream for our whole human family."
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The video was released hours after it was confirmed that the Pope would meet victims of clerical sex abuse during his Irish visit.
The Vatican said the meeting would not be announced until after it was over and that it would be up to victims if they wanted to speak afterwards.
The head of the Catholic Church has condemned the "atrocities" of child sex abuse by clerics and cover-ups in the Church.
He published a letter to the world's 1.2 billion Catholics on Monday, addressing failures to deal with abuse and calling for an end to the "culture of death".
Ireland is gearing up for its first papal visit in 40 years during which at least half a million people are expected to attend a special mass in Dublin's Phoenix Park.
The Pope's 36-hour visit will begin on Saturday morning and his itinerary also includes the Festival of Families concert in Dublin's Croke Park stadium and a trip to the Knock holy shrine in County Mayo.
As Father Jorge Bergoglio, he visited the Jesuit community at Milltown Park in Dublin in 1980.
Papal visit to Ireland: Itinerary highlights
Saturday 25 August
- 08:15 - Departure by plane from Rome for Dublin
- 10:30 - Arrival at Dublin Airport for official welcome
- 10:45 - Transfer to Áras an Uachtaráin (Irish president's residence)
- 11:15 - Welcome ceremony with President Michael D Higgins
- 12:10 - Arrival at Dublin Castle for meeting with authorities, civil society and diplomatic corps
- 15:30 - Visit to St Mary's Pro Cathedral
- 16:30 - Private visit to the Capuchin Day Centre, a centre for homeless people
- 19:45 - Preside at the Festival of Families at Croke Park stadium
Sunday 26 August
- 08:40 - Departure by plane for Knock
- 09:45 - Arrival at Knock Shrine for visit to the Apparition Chapel and recitation of the Angelus
- 11:15 - Departure by plane for Dublin
- 12:30 - Lunch with the Papal Delegation
- 15:00 - Closing Papal Mass of the World Meeting of Families in Phoenix Park followed by a meeting with the Irish bishops
- 18:30 - Farewell ceremony at Dublin Airport
- 18:45 - Departure by plane for Rome
- 23:00 - Arrival in Rome