It was the fifth such move in just over two weeks and raised to 2,791 the number of new settler homes announced since the start of the year, threatening to derail faltering US-brokered peace talks with the Palestinians.
Israel's rapid settlement expansion has angered Palestinian negotiators and drawn condemnation from the international community, threatening peace talks that US Secretary of State John Kerry kick-started in July.
EU envoy to Israel Lars Faaborg-Andersen said continued settlement building would isolate the Jewish state, which he warned would be held accountable for a failure of peace talks.
"If the talks are wrecked as a result of Israeli settlement announcements, then the blame will be put squarely on Israel's doorstep," he said.
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"You are eating away at the cake that you are discussing how to slice up."
Israeli Prime Minister Benjamin Netanyahu last week accused the EU of a "hypocritical" attitude toward the Middle East peace process, saying it should be more concerned by Palestinian militancy than Israeli housing construction.
"The addition of 256 housing units to the small, isolated settlement of Nofei Prat dramatically changes the settlement, expanding its size and population significantly. In fact, these planned units will nearly triple the size of Nofei Prat," Peace Now said in a statement.
Construction would be allowed to start "without further political approval or public awareness," it added.