Pope Francis on Sunday urged an end to the "increasingly unacceptable" Israeli-Palestinian conflict, calling on leaders to show "courage" to achieve a peace based on a two-state solution.
"The time has come to put an end to this situation which has become increasingly unacceptable," he said in the Judean town of Bethlehem where Christians believe Jesus was born.
"The time has come for everyone to find the courage... to forge a peace which rests on the acknowledgement by all of the right of two states to exist and to live in peace and security within internationally recognised borders."
Pope Francis arrived in Bethlehem Sunday to begin the most sensitive part of his three-day Middle East tour aimed at easing an ancient rift with Orthodox Christians and forging regional peace.
He made the short trip from Amman, where he began his visit Saturday, aboard a Jordanian military helicopter.
The pontiff appeared tired as he was helped down the steps to a red carpet welcome from local Palestinian Authority officials and priests.
Palestinian Authority head Mahmoud Abbas received him at his palace with a warm embrace.
Francis, who made an urgent appeal Saturday to end the bloodshed in Syria, has now taken his "pilgrimage of prayer" to Palestinian Authority-controlled areas. There he was to celebrate mass with 10,000 people in Bethlehem's packed Manger Square, near the site which Christians say was Jesus' birthplace.
He is scheduled to begin his official Israeli visit later Sunday.
Although Francis himself has said it will be a "purely religious trip," both Israel and the PA will be looking to use the visit to score a few political points.
The Vatican said the main reason for the visit was a meeting in Jerusalem with Bartholomew I, the Orthodox Patriarch of Constantinople, seeking to heal a nearly 1,000-year rift between the Orthodox and Roman Catholic churches.
But ahead of the trip, Vatican Secretary of State Cardinal Pietro Parolin defended the Palestinian Arabs' right to a "sovereign and independent" homeland and said he hoped Francis's visit would lead to "courageous decisions" for peace.
Since dawn, Catholic pilgrims filed past security barriers into Manger Square. The scene was dominated by stage where the pope was to say mass, decked with huge PLO and Vatican flags and adorned with a giant tableau depicting the birth of Jesus.
To get there, the crowd-loving pope will drive through the city in an open-top car, raising security concerns in a region racked by political and religious strife.
Meanwhile, in Jerusalem, police arrested 26 Jewish protesters at a site on Mount Zion where the pope will celebrate mass on Monday. Earlier this week, police imposed restraining orders on 15 activists, barring them from sites the pope will visit. Jewish groups are angry over persistent rumors that the Israel government is planning to hand over control of King David's Tomb to the Vatican, despite repeated denials by Israeli officials.
Overnight, police with sniffer dogs combed the narrow streets of the Old City, closely examining the stone alleyways down which the pontiff was to walk later Sunday.
In a separate development, Israel's foreign ministry confirmed that two of the three people shot dead in an attack Saturday on the Jewish museum in Brussels were Israeli tourists. The incident has drawn condemnation from top Israeli and European officials.
John Allen, an expert on the Vatican at the Boston Globe, said the pope was likely to "charm" both sides during the Israeli-PA leg of his visit.
"Francis comes in with a lot of political capital. He's sort of a new Nelson Mandela, a new moral authority on the world stage.
"The question is: can he spend that moral capital to shame both sides into talking to each other? You might be able to get a public commitment to resume dialogue. It's the most we can expect."
US-led peace talks between Israeli and Palestinian Authority negotiators collapsed last month amid bitter recriminations, ending a nine-month bid to reach a negotiated solution, with no political initiative on the horizon.
Travelling with the Argentine pontiff are two of his old friends from Buenos Aires - Rabbi Abraham Skorka and Islamic studies professor Omar Abboud - in a symbolic gesture of openness.
'Contribution to peace'
After celebrating mass, the pope will have lunch with several Palestinian Arab families then meet with children at the entrance to Dheishe refugee camp.
During the afternoon, he will take a short flight to Tel Aviv where he will be formally welcomed to Israel by President Shimon Peres before flying on to Jerusalem.
"I don't think the visit is going to bring the signing of a peace deal tomorrow... but I am sure that it will make a substantial contribution, because the pope respects all cultures and all religions," Peres told French daily Le Figaro.
It is inside Jerusalem's walled Old City that he will attend a special joint prayer service with Bartholomew in the Church of the Holy Sepulchre - venerated by Christians as the place of Jesus' crucifixion and resurrection.