Pope Francis on Saturday headed for a one-day visit to Bosnia aimed at bolstering reconciliation between Serb, Croat and Muslim communities.
The trip to Sarajevo comes 20 years after the end of a 1992-95 war that ripped the Balkan state apart and left it permanently divided along ethnic lines.
Adding to security jitters, Islamists claiming to be members of the Islamic State (IS) group called for jihad in the Balkans in a video widely reported on Friday by local media, although there appeared to be no explicit link to the visit.
More than a third of Bosnia's mostly Catholic Croats have left Bosnia since the war and the country of 3.8 million people is divided in two between a Bosnian Serb republic and a Croat-Muslim federation.
Sarajevo, once a beacon of multiculturalism, is also now largely split along ethnic lines.
Against that backdrop, Vatican officials believe Francis can have a positive impact by promoting the kind of inter-faith dialogue he holds dear.
Francis's plane left Rome airport shortly after 5:30 GMT for the pontiff's eighth trip abroad.
In a message to the residents of Sarajevo earlier this week, he wrote, "I come amongst you... to express my support for ecumenical and interfaith dialogue, and above all to encourage peaceful cohabitation in your country."
Pietro Parolin, the Vatican secretary of state who heads the Holy See's diplomacy, said Francis would visit in the spirit of a pilgrim, promoting dialogue and peace and hoping to raise spirits among Catholics.
"The consequences of war have been felt particularly by the Catholic community. In some parishes there are very few families left, many of them elderly," he said.
"In December the 20th anniversary of the war will be remembered but the traces and the wounds of war are still there."
Open air mass
The highlights of Francis's 10 hours in Sarajevo will be an open air mass for 65,000 people in the Olympic stadium and a meeting between the pontiff and representatives of the Catholic, Orthodox and Muslim communities, as well as the small Jewish community.
Around 40% of the population of Bosnia is of Islamic heritage, just over 30% are from the Serbian Orthodox tradition and around one in ten, almost uniquely Croats, describe themselves as Catholics.
The pope will also hear personal testimony from some of those who suffered during the war, including two priests and a nun.
Security will be high in a country that has become fertile ground for homegrown jihadists and the video will heighten concerns, although the Vatican has been insisting they do not see the trip as high-risk.
At least 5,000 police will be on duty and a total of 100,000 people are expected to turn out to get a glimpse of the Argentinian pontiff.
The visit comes a month after a Bosnian Islamist shot one policeman dead and injured two others in an attack in the northeast.
The incident led security minister Dragan Mektic to describe the terror threat in Bosnia as serious and growing, partly as a legacy of jihadists having come to the country to help Bosnian Muslim forces during the war.
Francis is the second pope to visit Sarajevo. Jean-Paul II famously visited during a severe snowstorm in 1997 and six years later, former Polish pope returned to Bosnia for a visit to the Bosnian Serb capital Banja Luka.