Pope Francis made a surprise stop on Sunday at the wall Palestinians abhor as a symbol of Israeli oppression, and later invited presidents from both sides of the divide to the Vatican to pray for peace.

In an image likely to become one of the most emblematic of his trip to the holy land, Francis rested his forehead against the concrete structure that separates Bethlehem from Jerusalem, and prayed silently as a child holding a Palestinian flag looked on.

He stood at a spot where someone had sprayed in red paint "Free Palestine". Above his head was graffiti in broken English reading: "Bethlehem look like Warsaw Ghetto", comparing the Palestinians' plight with that of the Jews under the Nazis.

Such imagery seemed likely to cause unease among Israel's leaders, who say the barrier, erected 10 years ago during a spate of Palestinian suicide bombings, is needed to secure its security. Palestinians see it as a bid by Israel to partition off territory and grab land they want for their future state.