Palestinian Christians near Bethlehem on Monday urged Pope Francis to speak up against an Israeli decision to build its controversial separation barrier on a route they say would cut off their community.

"We cry to your Holiness with a feeling of despair and urgency in order to keep alive our hope that justice and peace is still possible," said an open letter from the Christians of Beit Jala, a town near the West Bank city of Bethlehem.

"The Israeli military occupation that has already started building the 'famous wall' annexing Palestinian land... (is) separating Bethlehem as well as other regions from Jerusalem and our holy places," it said.

The letter came as Israel's President Shimon Peres was due to arrive in Italy on a three-day visit during which he would meet Pope Francis.

"We respectfully ask you to make use of this meeting to pass a strong message regarding the people of Palestine, and particularly the case of Beit Jala's Cremisan land," it said.

The letter added: "We need concrete actions in order to end Israel's impunity so we can live with dignity in our free state... Your holiness, your election brought us hope that things would change. We are still hopeful."

An Israeli court ruled last week in favour of constructing the so-called separation barrier through the 170-hectare Cremisan Valley, where many of Beit Jala's Christians work on the land and its vineyards.

The barrier's planned route would cut them off from the valley, and would effectively separate it from Jerusalem, which is five kilometres (three miles) away, locals say.

The International Court of Justice ruled in 2004 that parts of the barrier were illegal and should be torn down.

In the Cremisan area, the route of the barrier deviates sharply from the Green Line, the internationally-accepted line marking the divide between Israel and the territories it captured in the 1967 Six-Day War.

But Israel's defence ministry insists it protects Israelis and that the route is determined by "specific security considerations" of the area.

"Building the Wall in the Bethlehem area it's not only a violation of international law... it is also an attack against Palestinian social fabric and Palestinian Christian presence," said Nabil Shaath, a member of Palestinian president Mahmud Abbas's Fatah party.

"Separating Bethlehem from Jerusalem for the first time in history, stripping Palestinians, mainly Christians, from their land in order to build and expand Israeli colonial settlements, walls and checkpoints is a cruel crime that further closes the chances for peace," he said.