Israel’s plans to annex a swathe of occupied Palestinian territory are "illegal", said the United Nation’s High Commissioner for Human Rights, Michelle Bachelet.

Michelle Bachelet warned that such a move would have a disastrous impact on the rights of people across the region.

"Annexation is illegal. Period. Any annexation. Whether it is 30 per cent of the West Bank, or 5 per cent," Michelle Bachelet said in a statement on Monday, urging Israel to reverse its decision and retreat from a "dangerous path."

Bachelet added: "The precise consequences of annexation cannot be predicted. But they are likely to be disastrous for the Palestinians, for Israel itself, and for the wider region."

The Israeli government is expected to detail later this week how to implement its US-backed Middle East peace plan. The proposal, unveiled earlier this year, includes Israel annexing settlements in the West Bank and Jordan Valley.