"The defence ministry this morning installed the final concrete walls, completing a 42-kilometre wall between Tarkumia and Meitar," it said in a statement, referring to the Palestinian village of Tarkumia, northwest of Hebron, and an Israeli crossing adjacent to Meitar settlement, further south.
It did not say how much of the planned 712-kilometre network of towering concrete walls, barbed-wire fences, trenches and closed military roads was now complete.
A ministry spokeswoman did not immediately respond to a request for the information.
The Jewish state says the barrier, which it began building after a wave of Palestinian attacks in 2002, is crucial for its security, while Palestinians see it as a land grab of territory they want for a future state.
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Most of it runs inside the occupied West Bank.
In a non-binding decision, the International Court of Justice ruled in 2004 that construction of the barrier was illegal and, like the UN General Assembly, demanded it be dismantled.
Prime Minister Benjamin Netanyahu last March ordered that a gap in the barrier in the Tarkumia area be closed as a priority after a spike of Palestinian attacks inside Israel.