Pope Francis made a plea for peace on Sunday at the start of a pilgrimage to Bethlehem, the birthplace of Jesus, saying the prolonged Israel-Palestinian conflict had become unacceptable.

On the second leg of a three-day visit to the Middle East, Francis delighted his hosts by referring directly to the "state of Palestine", giving support for their bid for full statehood recognition in the face of a paralysed peace process.

However Francis, speaking at an official reception in the Palestinian-run city in the Israeli-occupied West Bank, made clear that a negotiated accord was needed, calling on leaders from both sides to show the necessary courage to forge a deal.

"For the good of all, there is a need to intensify efforts and initiatives aimed at creating the conditions for a stable peace based on justice, on the recognition of the rights of every individual, and on mutual security," he said.

Later, in an unscheduled stop, he descended from his popemobile when it drove past the hulking grey concrete wall that Israel erected 10 years ago during a Palestinian uprising, that divides Bethlehem from the adjacent Jerusalem.

Israel says the wall is needed for security reasons. The pope spent several minutes under the shadow of an Israeli watchtower and said a prayer, a Reuters witness said.

"Free Palestine", said graffiti near where he paused.

Church officials say his tour of the region is focused on religious issues. However, the stark dividing lines of the Middle East conflict are impossible to ignore, and the pope's every move will be scrutinised for meaning.

Francis flew by helicopter to Bethlehem, becoming the first pontiff to travel directly to the West Bank rather than enter via Israel, in another nod to Palestinian statehood aspirations.

He is due to travel to Israel later in the day for a swirl of meetings, before returning home on Monday, with some 8,000 police deployed in Jerusalem to guarantee his security.

Israeli police said they arrested 26 people who took part in a protest early on Sunday by Jewish nationalists at the Cenacle in Jerusalem, the traditional site of Jesus's Last Supper, where Francis is due to hold a Mass on Monday.

The protesters say the authorities are preparing to hand the Church the site, where some Jews believe King David is buried. The Israeli government has denied any such deal.

JESUS IN A KEFFIYEH

US-backed negotiations aimed at ending the conflict collapsed last month, with the Israelis accusing Palestinian President Mahmoud Abbas of sabotaging the talks by agreeing a unity deal with Hamas Islamists who run the Gaza Strip.

Standing alongside Abbas, Francis pointedly referred to him as "a man of peace and a peacemaker" before heading to Bethlehem's Manger Square, close to where Christians believe Jesus was born, to celebrate an open-air Mass.

A mural behind the altar showed Jesus, who was a Jew, swaddled in a Palestinian keffiyeh, with his father, Joseph, also wearing the black and white headdress, made famous by the late Palestinian leader Yasser Arafat.

After barely six hours in Bethlehem, Francis heads to Israel, but to avoid a diplomatic tangle, he has to get back in his helicopter and fly to Tel Aviv airport for a welcoming reception, rather than drive the short distance to Jerusalem.

Israel calls Jerusalem its eternal and undivided capital, having annexed Arab neighbourhoods seized in the 1967 war, including the Old City, the site of the main religious shrines. The rest of the world has not recognised the annexation.

From Tel Aviv, he will get back in his helicopter and fly to Jerusalem for what he has said is the purpose of the whole trip - to commemorate the 50th anniversary of a historic meeting of Catholic and Orthodox Christian leaders, who moved to end centuries of bitter divisions between the two churches.

The Vatican's yellow and white flags flutter from lampposts across the city, and posters of a smiling Francis have been strung up from numerous buildings, but that might be as much as many locals get to see of him.

His decision not to use a bullet-proof car means Israeli security officials are clearing the roads and creating numerous "sterile areas" ahead of his 24-hour stay in the city. - Reuters