B'Tselem says the annexations more than doubled the size of settlements
Israel has annexed thousands of hectares of West Bank land beside the barrier it is building, according to an Israeli rights group.
B'Tselem says the land has been taken with the justification that it is needed to protect Israeli settlements.
The group says some settlements have seized up to two and a half times more land than they have been designated by fencing it off or through intimidation.
Under international law the settlements in the West Bank are illegal.
This is disputed by Israel, which has settled about 450,000 people in the West Bank, including East Jerusalem.
Israel argues that its West Bank barrier is a security measure intended to stop suicide bombers, though Palestinians see the barrier as a means to grab land.
The International Court of Justice issued an advisory ruling in 2004 that the barrier breached international law where it is built on occupied territory and should be dismantled.
B'Tselem calculates that the annexation of the land has more than doubled the size of the settlements, with Palestinians, who still own the land, denied access.
The objective of these zones is to provide warning of an attack on a community, providing enough time to respond
It says that the unofficial closing off of land to Palestinians, around these settlements, has been going on for 30 years.
But what has been happening more recently is the Israeli military formalising the expansion of these settlements through what are called "special security areas".
The group has calculated that this has more than doubled the overall area of the settlements.
Palestinians, despite privately owning half the land, now have no access to it.
The Israeli authorities argue that these measures are for security, to protect against Palestinian attacks, and that they need only be temporary.
The Israel Defense Forces (IDF) said in a statement to the BBC that the security zones were needed to protect settlements. The IDF said the use of these zones had been approved a number of times by the Israeli Supreme Court and any building in them was illegal.
But B'Tselem insists that the security argument is specious: they say that settlers often move into the designated security buffer zones.
They also argue that it makes the agreed goal of a future Palestinian state all the more difficult to reach.