Pope Leo lamented during his first trip outside Italy as Catholic leader on Thursday that the world was seeing an unusual number of bloody conflicts, and warned that a third world war was being "fought piecemeal" with humanity's future at risk.

In his first speech given overseas since his election in May to lead the 1.4 billion-member Church, Leo, the first US pope, said "ambitions and choices that trample on justice and peace" were destabilising the world.

He told political leaders in Turkey that the world was experiencing "a heightened level of conflict on the global level, fuelled by prevailing strategies of economic and military power".

Trip marks 1,700th anniversary of Nicene Creed

"We must in no way give in to this," he pleaded at an event with President Tayyip Erdogan after they held a private meeting. "The future of humanity is at stake."

Speaking before the pope, Erdogan said that he welcomed the pope's "astute stance" on the Palestinian issue, and hoped the visit would be beneficial for humanity at a time of tension and uncertainty.

In September, Leo met Israeli President Isaac Herzog at the Vatican and raised the "tragic situation" in Gaza with him.

The first US pope chose mainly Muslim Turkey as his first overseas destination to mark the 1,700th anniversary of a landmark early Church council there that produced the Nicene Creed, still used by most of the world's Christians today.

Leo, 70, landed in the capital Ankara shortly after midday (0900 GMT) to begin a crowded three-day itinerary in Turkey before heading on to Lebanon. It will be closely watched as he makes his first speeches overseas and visits sensitive cultural sites.

Papal trips abroad draw global attention

Speaking to journalists aboard the papal flight from Rome, Leo said he wanted to use his first overseas trip to urge peace for the world, and to encourage people of different backgrounds to live together in harmony.

"We hope to... announce, transmit, proclaim how important peace is throughout the world," the pope said at the beginning of the three-hour flight. "And to invite all people to come together, to search for greater unity, greater harmony."

Foreign travel has become a major part of the modern papacy, with popes attracting international attention as they lead events with crowds sometimes in the millions, give foreign policy speeches and conduct international diplomacy.

"It's a very important trip because we do not know much yet about Leo's geopolitical views, and this is the first big chance for him to make them clear," Massimo Faggioli, an Italian academic who follows the Vatican, told Reuters.

Leo to meet orthodox patriarch

Leo was elected in May by the world's Catholic cardinals to succeed the late Pope Francis. A relative unknown on the world stage before his election, Leo spent decades as a missionary in Peru and only became a Vatican official in 2023.

Francis had been planning to visit Turkey and Lebanon but was unable to go because of his worsening health.

Francis, who led the global Church for 12 years, often said the conflicts raging across the globe reflected a new "piecemeal" world war and pleaded for the end of wars in Gaza, Ukraine, Iraq, Syria and across Africa, among others.

He will fly on Thursday evening to Istanbul, home to Patriarch Bartholomew, spiritual leader of the world's 260 million Orthodox Christians.

Orthodox and Catholic Christians split in the East-West Schism of 1054, but have generally sought in recent decades to build closer ties.

Leo and Bartholomew travel on Friday to Iznik, 140km (90 miles) southeast of Istanbul and once called Nicaea, where early churchmen formulated the Nicene Creed, which lays out what remain the core beliefs of most Christians today.

On the flight to Ankara, two journalists presented the American pope with pumpkin pies, a staple of the US Thanksgiving holiday that was also taking place on Thursday.

Peace will be key theme of Lebanese leg

Peace is expected to be a key theme of the pope's visit to Lebanon, which starts on Sunday.

Lebanon, which has the largest percentage of Christians in the Middle East, has been rocked by the spillover of the Gaza conflict.

Last Sunday, Israel killed the top military official in the Iran-backed Shi'ite Muslim militant group Hezbollah in an airstrike on a southern suburb of the Lebanese capital Beirut despite a year-long, US-brokered truce.

Vatican spokesman Matteo Bruni said on Monday that necessary security precautions were being taken to ensure the pope's safety in Lebanon, but he would not comment on specifics.

Leaders in Lebanon, which hosts one million Syrian and Palestinian refugees and is also struggling to recover after years of economic crisis, are worried Israel will dramatically escalate its strikes in the coming months and hope the papal visit might bring global attention to the country.