Israel's West Bank security barrier will cause serious human suffering, the UN has said in a report.
Palestinians say the barrier will cause hardship
The report says that the barrier will separate almost 700,000 Palestinians from their farms, jobs and schools.
Israel rejects the report - which it says is inaccurate - and argues that the barrier is necessary to prevent suicide bombers from entering Israel.
The BBC's David Chazan in Jerusalem says the route, not the barrier itself, is the cause of controversy.
The UN Office for the Co-Ordination of Humanitarian Affairs - the agency that wrote the report - and Israel disagree about how much Palestinian land will be separated from the bulk of the West Bank by the barrier.
The UN says it will carve off 14.5% of the West Bank and affect 680,000 Palestinians.
Israel says the barrier will have gates
But a senior Israeli Foreign Ministry official told the Reuters news agency it will cut off no more than 4%, leaving only 14,000 Palestinians west of the barrier.
Critics charge that the barrier - which is to be a combination of fence and wall - does not follow the existing border between Israel and the West Bank, known as the Green Line.
They say it represents a land grab by Israel, designed to influence future political boundaries.
Israel rejects the allegation, saying it is for security only. They say a similar barrier has prevented any suicide bombers from entering Israel from the Gaza Strip.
The government says the new UN report is based on an inaccurate idea of the route of the fence, and does not take into account that it will have gates so Palestinians can get to and from their homes.
An earlier UN report in September condemned the barrier as a land grab, and the UN General Assembly has criticised it.
Israel says the General Assembly has an anti-Israel bias due to its large Muslim and Arab membership.
The barrier, which is not yet completed, is expected to be about 700 kilometres long.
Tuesday's report makes no mention of suicide bombings or the Palestinian uprising that has been going on for more than three years.