More than a third of the Jewish settlements in the West Bank are built on privately owned Palestinian land, an Israeli campaign group has reported.
Peace Now: Largest settlement is built on private Palestinian land
Peace Now says nearly 40% of the land the settlements sit on is, according to official data, "effectively stolen" from Palestinian landowners.
This, the group says, is a violation of Israel's own laws.
Settlements in the occupied West Bank are illegal under international law, although Israel rejects this.
About 430,000 Jews live in these residential areas in the West Bank and East Jerusalem.
Peace Now called on the Israeli government to return the private land to its Palestinian owners.
In recent years the Israeli government has said repeatedly that it respects Palestinian property rights in the West Bank.
An Israeli official has said the government is reviewing the report.
130 settlements were constructed either entirely or partially on private Palestinian land
19,800 acres of the land used by the settlements, nearly 40% of the total, is private Palestinian land
86.4% of Maale Adumim is built on privately-owned land
Source: Peace Now
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The data on which the findings are based comes from a 2004 survey by the Civil Administration, which manages the civilian aspects of Israel's occupation of the West Bank.
The data was leaked to Peace Now via an official in the Civil Administration. The group says the government had refused to give this information to it.
The group says that the data it has received has been "hidden by the State for many years, for fear that the revelation of these facts could damage its international relations".
According to the report, 86.4% of the Maale Adumim settlement block, the largest in the West Bank, is built on private Palestinian land, and not on what the Israeli government refers to as "state land".
The settlement is home to 32,372 people and lies due east of Jerusalem.
'Violation' of Israeli law
"The claim by the State and settlers that the settlements have been constructed on state land is misleading and false," Peace Now says.
Illegal under international law according to Fourth Geneva Convention (article 49), which prohibits an occupying power transferring citizens from its own territory to occupied territory
Israel argues international conventions relating to occupied land do not apply to West Bank because it was not under the legitimate sovereignty of any state before 1967
"The vast majority of settlement construction was done against the law of the land and the Supreme Court ruling and therefore unauthorised.
"[The data] indicates the direct violation of Israeli law carried out by the State itself, driven by the architects and leaders of the settlement movement."
In 1979 the Israeli High Court forbade the establishment of settlements on privately-owned Palestinian that has been seized by Israel for military purposes.
The Israeli-Palestinian conflict is at its core a conflict over land and in the West Bank property rights, BBC Jerusalem correspondent Crispin Thorold says.
This is the area which Palestinians want to be the basis of a future independent state.
If confirmed the findings could have major implications for any future peace deal.
Some of the settlements that the Israeli government wants to be included within its final borders are built on land overwhelmingly owned by Palestinian individuals.
Peace Now is an Israeli group that monitors Israel settlements in the West Bank.
The oldest peace movement in Israel, it advocates the setting up of a Palestinian state on land occupied by Israel in 1967.